Diffractive luminaires

ABSTRACT

Extended area lighting devices, which are useful e.g. as luminaires, include a light guide and diffractive surface features on a major surface of the light guide. The diffractive surface features are tailored to extract guided-mode light from the light guide. The light guides can be combined with other components and features such as light source(s) to inject guided-mode light into the light guide, light source(s) to project light through the light guide as non-guided-mode light, a framework of interconnected support members (attached to multiple such light guides), and/or a patterned low index subsurface layer that selectively blocks some guided mode light from reaching the diffractive surface features, to provide unique and useful lighting devices. Related optical devices, and optical films having diffractive features that can be used to construct such devices and light guides, are also disclosed.

FIELD OF THE INVENTION

This invention relates generally to lighting devices, with particularapplication to lighting devices that incorporate a light guide anddiffractive elements to couple guided-mode light out of the light guide.The invention also relates to associated articles, systems, and methods.

BACKGROUND

Extended area lighting devices that use a light guide to spread lightfrom discrete edge-mounted CCFL or LED light sources over the extendedarea of the light guide are known. Edge-lit backlights used in liquidcrystal displays (LCDs) are a major example of such lighting devices.Ordinarily, it is important for such lighting devices to have a colorand brightness that are uniform, or at least slowly varying, as afunction of position on the extended area output surface. It is alsoordinarily important for such lighting devices to emit light of asubstantially white color, so that the filtering action of the liquidcrystal panel can produce full color pixels and pictures ranging fromblue through red.

In order to extract guided-mode light out of the light guide, edge-litbacklights often configure a major surface of the light guide to have aprinted pattern of diffusive paint or other scattering material, or tohave a structured surface e.g. as provided by a series of grooves orprisms whose facets are designed to change the direction of light byrefraction or reflection. It is not common to extract guided-mode lightout of the light guide using diffractive grooves or prisms on the majorsurface, because diffraction has a strong wavelength dependence whichcould easily produce a highly colored appearance, and a highly coloredappearance is unacceptable in most end-use applications.

BRIEF SUMMARY

We have developed a new family of extended area lighting devices thatextract light from an extended light guide using diffractive surfacefeatures on a major surface of the light guide. The diffractive surfacefeatures interact with guided-mode light to couple the light out of thelight guide.

The light guides can be combined with other components and features suchas a light source to inject guided-mode light into the light guide, alight source to project light through the light guide as non-guided-modelight, a framework of interconnected support members (attached tomultiple such light guides), and/or a patterned low index subsurfacelayer that selectively blocks some guided mode light from reaching thediffractive surface features, to provide unique and useful lightingdevices. Related optical devices, and optical films having diffractivefeatures that can be used to construct such devices and light guides,are also disclosed.

The lighting devices may be used as luminaires to provide generallighting or decorative lighting in an office space or other living orworking environment. Alternatively, the lighting devices may be used inother applications such as security applications. The diffractivesurface features used in these devices can provide low opticaldistortion for non-guided-mode light that propagates through the lightguide, to permit viewing of objects through the light guide.

We describe herein, inter alia, lighting devices such as luminaires thatinclude a light guide, a first light source, and a second light source.The light guide has opposed major surfaces, and at least one of themajor surfaces has diffractive surface features therein adapted tocouple guided-mode light out of the light guide. The first light sourceis configured to inject light into the light guide. The second lightsource is configured to project light through the light guide asnon-guided-mode light.

The light guide may have a low optical distortion such that the lightprojected by the second light source is not substantially deviated bythe light guide. The opposed major surfaces of the light guide mayinclude a first major surface opposed to a second major surface, and theprojected light from the second light source may enter the first majorsurface and exit the second major surface, and the diffractive surfacefeatures may be configured to couple more guided-mode light out of thesecond major surface than out of the first major surface.

We also disclose lighting devices such as luminaires that include aframework, a plurality of light guides, and a plurality of lightsources. The framework includes a plurality of interconnected supportmembers, and the plurality of light guides are attached to theframework. Each of the light guides has opposed major surfaces, and atleast one of the major surfaces of each light guide has diffractivesurface features therein adapted to couple guided-mode light out of thelight guide. The plurality of light sources are disposed on and/or inthe support members, and the light sources are distributed to injectlight into all of the light guides.

At least some of the light guides may have a low optical distortion suchthat objects can be viewed through such light guides. Further, at leastsome of the light guides, or all of the light guides, may besubstantially co-planar. In some cases, at least some of the lightguides may be arranged in a helix, or may be arranged to collectivelyform a concave shape. In some cases, the light guides may collectivelyform a 3-dimensional structure that is closed and hollow.

For at least some of the light guides, the diffractive surface featuresmay couple guided-mode light preferentially out of one of the opposedmajor surfaces, designated an output major surface. The output majorsurfaces for such light guides may face generally in a same direction,e.g., surface normal vectors of such light guides may have a scalarproduct that is positive.

The plurality of light sources may include light sources ofsubstantially different first, second, and third output colors, such asred, green, and blue, and the light sources may be distributed such thatat least a first one of the light guides is illuminated predominantlywith light source(s) of the first output color, at least a second one ofthe light guides is illuminated predominantly with light source(s) ofthe second output color, and at least a third one of the light guides isilluminated predominantly with light source(s) of the third outputcolor.

We also disclose lighting devices such as luminaires that include atube-shaped light guide and a first light source configured to injectlight into the light guide. The light guide has a first major surface onwhich diffractive surface features are formed, the diffractive surfacefeatures adapted to couple guided-mode light out of the light guide. Thetube-shaped light guide may be hollow and may have two open ends and anannular-shaped side surface proximate one of the open ends. The firstlight source may be disposed to inject light into the annular-shapedside surface. The tube-shaped light guide may be substantiallycylindrical in shape, or substantially conical in shape.

We also disclose optical devices that include a light guide and apatterned low index subsurface layer. The light guide has opposed majorsurfaces, and at least one of the major surfaces has diffractive surfacefeatures therein adapted to couple guided-mode light out of the lightguide. The patterned low index subsurface layer is configured toselectively block some guided mode light from reaching at least some ofthe diffractive surface features. The patterned low index subsurfacelayer may include first and second layer portions, and the first layerportions may include a nanovoided polymeric material and the secondlayer portions may include the same nanovoided polymeric material and anadditional material. Alternatively, the second layer portions may becomposed of a polymer material that is not nanovoided. Furthermore,patterned low index subsurface layer may be composed of one or morepolymer materials none of which are nanovoided. The optical device mayinclude a light source disposed to inject light into the light guide.

Related methods, systems, and articles are also discussed.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side or sectional view of a lighting deviceutilizing diffractive surface features on a major surface of a lightguide;

FIG. 2 is a schematic side or sectional view of a light guide with adiscrete light source injecting light into the light guide anddiffractive surface features coupling guided-mode light out of the lightguide;

FIG. 3 is a graph of intensity versus polar angle of integrated opticalpower density for light extracted from a light guide using lineardiffractive surface features;

FIG. 4 is a micrograph of a replicated diffractive surface useful forlight extraction from a light guide;

FIG. 5 is a conoscopic plot of measured intensity as a function of polarand azimuthal angle for a lighting device that used diffractive surfacestructures as shown in FIG. 4;

FIG. 5 a is a graph of measured luminance versus polar angle along aparticular observation plane for the conoscopic plot of FIG. 5;

FIG. 6 is a schematic side or sectional view of a light guide havingasymmetric or blazed diffractive surface structures;

FIG. 7 is a graph of calculated extraction efficiency for the surfacestructures of FIG. 6;

FIG. 8 is a schematic side or sectional view of a lighting device thatincludes a plurality of light guides in a stacked or layeredarrangement;

FIG. 9 is a schematic perspective view of a lighting device thatincludes different diffractive surface features disposed on oppositemajor surfaces of the light guide and tailored for different coloredlight sources;

FIGS. 10 and 11 are schematic side or sectional views of light guideswith diffractive surface features, the diffractive surface featuresincluding groups of surface features of different pitches;

FIG. 12 is a schematic front or plan view of a light guide havingdiffractive surface structures formed into a spiral;

FIG. 12 a is a detail of the light guide of FIG. 12;

FIG. 13 is a schematic front, plan, or sectional view of a portion of alighting device including a light guide, discrete light sources disposedto inject light into the light guide, and support structure;

FIG. 14 is a schematic front or plan view of a flat pie-shaped lightguide having diffractive surface structures of equal curvature;

FIGS. 15 a and 15 b are schematic side or sectional views of a lightingdevice that has a colorful appearance when observed by an ordinary user,but that provides substantially white light illumination at a remotereference surface of interest;

FIG. 16 is a schematic side or sectional view of a lighting device inwhich relative widths or areas of three different types of diffractivesurface features are selected in accordance with a light source whosespectral intensity distribution has a high blue content;

FIG. 17 is a schematic side or sectional view of a lighting devicesimilar to that of FIG. 16, but where a light source is used whosespectral intensity distribution does not have the unusually high bluecontent, and the relative widths or areas of the three different typesof diffractive surface features are adjusted accordingly;

FIG. 17 a is a schematic representation of the output spectrum of acollection of red, green, and blue LEDs;

FIGS. 18 and 19 are schematic side or sectional views of additionallight guides with patterned printing, these light guides also having apatterned low index subsurface layer;

FIG. 18 a is a schematic cross sectional view of an exemplary patternedlow index subsurface layer;

FIG. 20 is a schematic side or sectional view of a lighting device thatcombines light extracted from the light guide by diffractive surfacefeatures with light projected through the light guide as non-guided-modelight;

FIG. 20 a is a schematic side or sectional view of a lighting devicesimilar to that of FIG. 20, but where the non-guided-mode lightprojected through the light guide is indirect illumination provided byreflected light;

FIG. 21 is a schematic front or plan view of a lighting device thatincludes a group of flat pie-shaped light guides and discrete lightsources;

FIGS. 22 and 23 are schematic front or plan views of lighting devicesthat include groups of triangle-shaped light guides;

FIGS. 24 and 25 show details of lighting devices in which a plurality oflight guides are attached to a framework of interconnected supportmembers, the support members containing a plurality of light sources toinject light into the light guides;

FIGS. 26 through 30 are schematic front or plan views of more lightingdevices each of which includes multiple light guides connected together;

FIG. 31 is a schematic side or sectional view of a lighting device inwhich the plurality of light guides are arranged to be substantiallyco-planar;

FIGS. 32 and 33 are schematic side or sectional views of lightingdevices in which the plurality of light guides are not arranged to beco-planar, but rather are arranged to collectively form a concave shape;

FIG. 34 is a schematic perspective view used to show that, for lightingdevices that contain multiple light guides, the light guides can bearranged in a helix;

FIGS. 35 through 38 are schematic perspective views of lighting devicesin which the multiple light guides are arranged to collectively form3-dimensional structures that are closed and hollow;

FIGS. 39 a through 39 c are schematic perspective views of non-flatlight guides that may be used in the disclosed lighting devices;

FIGS. 39 d and 39 e are schematic perspective views of non-flat lightguides which are also tube-shaped, and which can be used in thedisclosed lighting devices;

FIG. 40 is a schematic perspective view of a lighting device thatincludes multiple light guides that are suspended in close proximity toeach other;

FIG. 41 a is a photograph of a lighting device that was constructedusing a circular light guide having curved diffractive surfacestructures, the lighting device photographed from an oblique viewingangle with ambient light on and the discrete light sources of thelighting device turned off;

FIG. 41 b is a photograph of the lighting device of FIG. 41 a, but withambient light off and the discrete light sources of the lighting deviceturned on, and at a slightly more oblique viewing angle, and withselected small areas or spots on the surface of the lighting deviceidentified and labeled;

FIG. 41 c is a graph of CIE chromaticity coordinates for the selectedspots of FIG. 41 b;

FIG. 42 a is a schematic view of a setup used for measuring the opticalproperties of a reference surface illuminated by the lighting device ofFIG. 41 b;

FIG. 42 b is a graph of measured CIE chromaticity coordinates forselected spots representative of illuminated measurement portions forthree different positions of the reference surface.

FIG. 43 is a photograph (with a magnified schematic inset) of a randomgradient dot pattern similar to one used to form a patterned low indexsubsurface layer for a lighting device;

FIG. 44 a is a photograph of a lighting device having a rectangularlight guide, curved diffractive surface features, and a patterned lowindex subsurface layer (similar to that shown in FIG. 43);

FIG. 44 b is a photograph of the lighting device of FIG. 44 a at anoblique viewing angle; and

FIG. 45 is a photograph of another lighting device that was constructedand tested.

In the figures, like reference numerals designate like elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As mentioned above, we have found that unique lighting devices, suitablefor use for example as luminaires for general lighting or decorativelighting applications, can be made by combining an extended area lightguide with other components or features, where the light guide includesdiffractive surface features formed on a major surface thereof to coupleguided-mode light out of the light guide. The other components andfeatures may include one or more of: discrete and/or extended lightsource(s) to inject guided-mode light into the light guide; lightsource(s) to project light through the light guide as non-guided-modelight; a patterned low index subsurface layer that selectively blockssome guided mode light from reaching the diffractive surface features;other light guides having diffractive surface features formed thereon; aframework of interconnected support members, which may be attached tomultiple such light guides and may contain light sources to inject lightinto the light guides; different shapes for the light guide, includingcurved shapes and other non-flat shapes, and hollow tubular shapes.

In some cases, out-coupled light from the light guide may exhibit a bandor pattern of bands whose apparent shape changes with viewing position.The bands may have a 3-dimensional appearance for at least some viewingpositions.

In some cases, a patterned light transmissive layer may be included thatoptically contacts some diffractive surface features but not otherdiffractive surface features. The patterned layer may define indicia,and the diffractive features may provide low distortion for viewingobjects through the light guide such that the indicia is not readilyapparent to users when guided-mode light does not propagate within thelight guide.

In some cases, the diffractive surface features may include diffractivefeatures of different pitches in non-overlapping regions of the majorsurface tailored to extract guided-mode light of different colors fromthe light guide in different directions. The diffractive features mayextract light such that an ordinary user observes substantiallydifferent colors in different regions of the light guide, providing acolorful appearance. Notwithstanding this, the diffractive features mayalso extract light such that the lighting device illuminates a referencesurface, disposed at an intermediate distance from the light guide, withillumination light that is substantially uniform in color and, ifdesired, substantially white.

An exemplary lighting device 110 is shown in schematic side or sectionalview in FIG. 1. The lighting device 110 includes an extended area lightguide 112 and discrete light sources 114 a, 114 b. The lighting device110 may be mounted in any desired configuration but in this case it isshown mounted physically above the user 120, e.g. in or near a ceilingof a room or building. If desired, the device 110 may be designed toprovide substantially uniform white light illumination on a surface 122such as a tabletop or floor. However, when the user 120 looks directlyat the device 110, the user may see a pattern of substantially differentcolors across the emitting area of the device 110. The pattern of colorsis due at least in part to guided-mode light of different wavelengths orcolors being extracted from the light guide by the diffractive surfacefeatures at different angles, or, more precisely, in different angulardistributions.

When looking directly at the device 110, the user may also see one ormore bands having a 3-dimensional appearance in the emitting area of thedevice. A given band is the result of the interaction of light emittedfrom one of the discrete light sources and diffractive surface featureson one or both major surfaces of the light guide. Alternatively, a givenband may be the result of the interaction of light reflected or absorbedby a localized region of high or low reflectivity in a non-uniformreflective structure extending along a side surface of the light guide.Details of such bands are described in commonly assigned patentapplication publication US 2014/0043846 (Yang et al.).

The user may also in some cases see indicia or other spatial patterns inthe emitting area of the device resulting from the patterned printing ofthe diffractive surface features. The patterned printing provides asecond light transmissive medium in optical contact with somediffractive surface features on at least one major surface of the lightguide. Other diffractive surface features on the same major surface arein optical contact with a different first light transmissive medium.Details of such indicia are described in commonly assigned U.S. Pat. No.8,834,004 (Thompson et al.).

In addition to the pattern of colors, the indicia, and the bands in theemitting area of the device, the user 120 may also observe objects suchas object 124 through the light guide 112 with little or no opticaldistortion. Light emitted by or reflected by such objects is able topropagate through the light guide as non-guided-mode light, only a smallamount of which is deflected by the diffractive surface features.

The light guide 112 is extended along two in-plane directions, shown inFIG. 1 as an x- and y-axis of a Cartesian coordinate system, so that thelight guide has opposed major surfaces 112 a, 112 b, as well as sidesurfaces 112 c, 112 d. Diffractive surface features 113 are provided onat least one of the major surfaces of the light guide 112, such assurface 112 a as shown in the figure, or in other embodiments surface112 b, or both surfaces 112 a and 112 b. In any case, the diffractivesurface features are tailored to couple guided-mode light out of thelight guide by diffraction. The guided-mode light is shown in the figureas light 116, and out-coupled light emitted from the light guide isshown as light 117 a, 117 b. Light 117 a passes through the surface 112a in the general direction of the user 120 or surface 122, and light 117b passes through the surface 112 b in the general direction away fromthe user 120 or surface 122. In some cases the lighting device 110 maybe mounted so that the light 117 b provides indirect illumination to theroom, e.g. by redirecting the light 117 b back into the room byreflection from the ceiling or from another reflective member.

In this regard, a reflective film or layer may be applied to all or aportion of the surface 112 b, or it may be positioned near the surface112 b, so as to redirect the light 117 b so it emerges from the surface112 a. The reflective film may reflect light diffusely, spectrally, orsemi-spectrally, and may reflect light uniformly or non-uniformly as afunction of wavelength, and it may reflect normally incident lightuniformly or non-uniformly as a function of polarization. The reflectivefilm may for example be or comprise: white paint or paints of any othercolor; high reflectivity mirror films, e.g., films with metal coatingssuch as aluminum, silver, nickel, or the like, or non-metallic mirrorfilms such as 3M™ Vikuiti™ ESR; multilayer optical films having organic(e.g. polymeric) or inorganic constituent optical layers with a layerthickness profile tailored to reflect light over some or all of thevisible spectrum at normal incidence or at another desired incidenceangle; ESR films with diffuse coatings; white reflectors having glossysurfaces; reflectors with brushed metal surfaces, including films withmetal coatings whose surface is roughened to provide semi-specular ordiffuse reflectivity; reflectors with structured surfaces;microcavitated PET films; 3M™ Light Enhancement Films; and/or reflectivepolarizing films, including but not limited to Vikuiti™ DiffuseReflective Polarizer Film (DRPF), Vikuiti™ Dual Brightness EnhancementFilm (DBEF), Vikuiti™ Dual Brightness Enhancement Film II (DBEF II), andmultilayer optical films having different reflectivities for normallyincident light of different polarizations but an average reflectivity ofgreater than 50% for such normally incident light, over some or all ofthe visible spectrum. See also the optical films disclosed in: US2008/0037127 (Weber), “Wide angle Mirror System”; US 2010/0165660 (Weberet al.), “Backlight and Display System Using Same”; US 2010/0238686(Weber et al.), “Recycling Backlights With Semi-Specular Components”; US2011/0222295 (Weber et al.), “Multilayer Optical Film with OutputConfinement in Both Polar and Azimuthal Directions and RelatedConstructions”; US 2011/0279997 (Weber et al.), “Reflective FilmCombinations with Output Confinement in Both Polar and AzimuthalDirections and Related Constructions”; WO 2008/144644 (Weber et al.),“Semi-Specular Components in Hollow Cavity Light Recycling Backlights”;and WO 2008/144656 (Weber et al.), “Light Recycling Hollow Cavity TypeDisplay Backlight”.

The light guide 112 may be physically thick or thin, but it ispreferably thick enough to support a large number of guided modes andfurthermore thick enough to efficiently couple to the emitting area ofthe discrete light sources. The light guide may, for example, have aphysical thickness in a range from 0.2 to 20 mm, or from 2 to 10 mm. Thethickness may be constant and uniform, or it may change as a function ofposition, as with a tapered or wedged light guide. If tapered, the lightguide may be tapered in only one in-plane direction, e.g. either the x-or the y-axis, or it may be tapered in both principal in-planedirections.

The light guide may be substantially flat or planar, ignoring smallamplitude surface variability associated with, e.g., diffractive surfacestructures. In some cases, however, the light guide may be non-flat,including simply curved, i.e., curved along only one principal in-planedirection, or complex curved, i.e., curved along both principal in-planedirections. The light guide may be entirely flat, entirely non-flat, orflat in some areas and non-flat in other areas. For light guides thatare non-flat along a particular in-plane direction, the cross-sectionalprofile along such a direction may be, for example, a simple arc, ormore complex non-straight contours. In some cases the light guide maydeviate greatly from a flat structure, e.g., the light guide may be inthe form of a solid or a hollow truncated hollow cone, wherein lightinjection can occur at the large end or the small end of the truncatedcone, as desired.

Whether or not the light guide 112 is flat, the light guide may have anouter boundary or edge whose shape, when the light guide is seen in planview, is curved, or piecewise flat (polygonal), or a combination ofpiecewise flat and curved. Examples of curved shapes are shapes withcontinuous arcs, such as circles, ovals, and ellipses, and shapes withdiscontinuous or undulating arcs, such as a sinusoid or sinusoid-likecontour. Examples of piecewise flat shapes are triangles, quadrilaterals(e.g., squares, rectangles, rhombuses, parallelograms, trapezoids),pentagons, hexagons, octagons, and so forth. The piecewise flat shapescan provide a straight or flat side surface or edge for light injectionfrom the discrete light sources, while curved shapes provide curved sidesurfaces for light injection.

The light guide is typically relatively rigid and self-supporting sothat it does not substantially bend or deform under its own weight, butflexible light guides can also be used and may, if desired, be held inplace using a support structure or frame, for example. The light guidemay have a unitary construction, or it may be made from a plurality ofcomponents attached to each other with no significant intervening airgaps, e.g., a thin structured surface film attached to a flat, smoothmajor surface of a thicker plate using a clear optical adhesive.

The light guide may be made of any suitable low loss light-transmissivematerial(s), such as glasses, plastics, or combinations thereof.Materials that are low loss, e.g., low absorption and low scatteringover visible wavelengths, are desirable so that guided-mode light canpropagate from one side surface completely across the light guide withabsorption/scattering losses that are small compared to losses due toout-coupling of such light by the diffractive surface features.Exemplary materials include suitable: glasses; acrylics; polycarbonates;polyurethanes; cyclo-olefin polymer/copolymers, including Zeonex™ andZeonor™ materials sold by Zeon Chemicals L.P, Louisville, Ky.; siliconesand elastomers; and pressure sensitive adhesives (PSAs) and otheradhesives, including silicone adhesives, 3M™ VHB™ conformable acrylicfoam tapes, and 3M™ OCA™ optically clear adhesives.

The device 110 also includes one or more discrete light sources 114 a,114 b, which are preferably mounted at an edge or side surface of thelight guide 112. The sources are discrete and small in size relative tothe in-plane dimension (length or width) of the light guide. However,light sources that are discrete or limited in size need not be used, andmay be replaced if desired with non-discrete light sources, includinglight sources whose emitting area is long and/or wide with respect tocorresponding dimensions of the side surface of the light guide. Thesources 114 a, 114 b are preferably solid state light sources such aslight emitting diodes (LEDs), but other suitable light sources can alsobe used.

In this regard, “light emitting diode” or “LED” refers to a diode thatemits light, whether visible, ultraviolet, or infrared, although in mostpractical embodiments the emitted light will have a peak wavelength inthe visible spectrum, e.g. from about 400 to 700 nm. The term LEDincludes incoherent encased or encapsulated semiconductor devicesmarketed as “LEDs”, whether of the conventional or super radiantvariety, as well as coherent semiconductor devices such as laser diodes,including but not limited to vertical cavity surface emitting lasers(VCSELs). An “LED die” is an LED in its most basic form, i.e., in theform of an individual component or chip made by semiconductor processingprocedures. For example, the LED die may be formed from a combination ofone or more Group III elements and of one or more Group V elements(III-V semiconductor). The component or chip can include electricalcontacts suitable for application of power to energize the device.Examples include wire bonding, tape automated bonding (TAB), orflip-chip bonding. The individual layers and other functional elementsof the component or chip are typically formed on the wafer scale, andthe finished wafer can then be diced into individual piece parts toyield a multiplicity of LED dies. The LED die may be configured forsurface mount, chip-on-board, or other known mounting configurations.Some packaged LEDs are made by forming a polymer encapsulant over an LEDdie and an associated reflector cup. Some packaged LEDs also include oneor more phosphor materials that are excited by an ultraviolet or shortwavelength visible LED die, and fluoresce at one or more wavelengths inthe visible spectrum. An “LED” for purposes of this application shouldalso be considered to include organic light emitting diodes, commonlyreferred to as OLEDs.

Light emitted by the sources such as sources 114 a, 114 b is injectedinto the light guide to provide guided-mode light, i.e., light that ispredominantly trapped in the light guide by total internal reflection(TIR), ignoring the effect of any diffractive surface features. Thelight emitted by each individual source is visible, and may be broadband (e.g. white) or narrow band (e.g. colored such as red, yellow,green, blue). If colored narrow band sources are used, different colorscan be combined to provide an overall white light illumination on thesurface 122, or the colors can be uniform, or different from each otherbut combined in such a way as to provide a decorative colored(non-white) illumination on the surface 122.

Diffractive surface features 113 are provided on at least one majorsurface of the light guide. These surface features or structures may beexposed to air, or planarized with a tangible material such as a lowrefractive index material, or both (some exposed to air, someplanarized) in a patterned arrangement. As discussed elsewhere herein,the diffractive surface features are sized and otherwise configured tocouple guided-mode light out of the light guide by diffraction, suchthat different wavelengths are coupled out differently, e.g. indifferent amounts, different directions, and different angulardistributions. The diffractive surface features may be tailored so thatlight from the edge-mounted light sources is emitted substantiallyequally from both major surfaces 112 a, 112 b of the light guide, orinstead so that the light is preferentially emitted from one of themajor surfaces, such as surface 112 a, which may then be designated theoutput surface of the light guide. In the latter case, the device may bemounted in a specific orientation so as to efficiently illuminate aroom, workspace, or other surface of interest.

Although the diffractive surface features couple guided-mode light outof the light guide, the light guide and the diffractive surface featuresare preferably tailored so that non-guided-mode light, e.g., lightoriginating from a source or object behind the light guide and incidenton one of the major surfaces of the light guide, is minimally deviated(whether by diffraction or refraction) such that objects can be viewedthrough the light guide with low distortion. The low distortion mayprovide both aesthetic and utilitarian benefits. In FIG. 1, thedistortion is low enough so that the user 120 can view and recognize theobject 124 through the light guide 112. The object 124 may be theceiling or another neighboring structure which neither generates lightnor is part of the lighting device 110. Alternatively, the object 124may generate light and may be a part of the lighting device 110, forexample, it may be another edge-lit light guide with its own diffractivesurface features, or it may be a more conventional light source such asa spotlight or light bulb with no diffractive surface features butconnected to the light guide 112 and mounted such that most or at leastsome of the light it emits is directed through the light guide 112. Theillumination provided by the additional light source may be direct orindirect, as shown below in connection with FIGS. 20 and 20 a.Furthermore, the object 124 may be or include a graphic film disposednear or attached to the device 110.

The diffractive surface features 113 may be present over substantiallyall of the major surface 112 a, or only a portion of the surface. If thediffractive surface features cover only certain portions of the surface,light from the edge-mounted light sources may be emitted from the lightguide only in those portions.

Additional aspects of the diffractive surface features are discussedfurther below. In some cases, the diffractive surface features and thelight sources may be tailored to yield a lighting device wherein anordinary user of the device observes substantially different colors indifferent regions of the light guide, for a colorful aestheticappearance, while at the same time providing illumination of asubstantially uniform color (e.g. a uniform white color) at a referencesurface of interest disposed perpendicular to an optical axis of thelight guide and at an intermediate distance D from the light guide. Thedistance D may be expressed in terms of a characteristic in-planedimension L of the light guide. For example, D may be at least 2*L butno more than 50*L, and L may be a maximum, minimum, or average in-planedimension of the light guide. The distance D may additionally oralternatively be at least 0.2 meters but no more than 15 meters.

The substantially uniform color may be substantially white, or it may beanother desired color. Light that is “substantially white” may refer toan area on the CIE x,y chromaticity diagram whose boundary is defined bytwelve color points: (0.305, 0.265), (0.29, 0.340), (0.330, 0.382),(0.375, 0.415), (0.425, 0.440), (0.470, 0.450), (0.530, 0.450), (0.530,0.380), (0.470, 0.375), (0.425, 0.360), (0.375, 0.335), (0.340, 0.305).The substantially different colors in different regions of the lightguide may include at least two colors separated from each other on a CIEx,y chromaticity diagram by more than a first color difference. Thefirst color difference may be 0.12, or 0.15, or 0.2. The illumination onthe reference surface may have a maximum value Imax, and thesubstantially uniform color may be characterized over a measurementportion of the reference surface at which the illumination provides anilluminance of at least Imax/e, where e is the mathematical constantequal to the base of the natural logarithm function. For substantiallyuniform color, no two points within the measurement portion areseparated from each other on the CIE x,y chromaticity diagram by morethan a second color difference, where the second color difference is0.08, or 0.07, or 0.06. The colorful appearance may be provided even incases where every light source disposed to inject light into the lightguide emits substantially white light. Further details of lightingdevices tailored to provide uniform color illumination with a lightguide having as colorful appearance are described in commonly assignedpatent application publication US 2014/0043847 (Yang et al.).

In some cases, at least some of the diffractive surface features mayoptionally be non-straight in plan view, and light propagating withinthe light guide may interact with the diffractive surface features toproduce at least one band that intersects the non-straight diffractivesurface features. The band may be a bright band, or, in some cases, adark band. The band changes in appearance (e.g. shape) as a function ofthe viewing position of an observer 120 relative to the lighting device110. The non-straight diffractive features may be, for example, curvedor segmented in shape, or may have an undulating or disjointed shapecomprising curves and/or segments. However, in some cases, some or allof the diffractive surface features on one or both of the major surfacesof the light guide may be straight in plan view. Bright and/or darkbands can also be generated with the straight diffractive surfacefeatures when discrete light sources and/or discrete absorbers are used,but the shapes of such bands may not change curvature as a function ofviewing position.

The lighting device 110, and the other lighting devices disclosedherein, can be used as a luminaire or similar lighting device forgeneral illumination purposes or the like. The luminaire may be mountedin any desired position and orientation, e.g., on, within, or near aceiling of a room, or on, within, or near a wall of a room, or mountedon a post, stand, or other support structure. The luminaire may beoriented parallel to the ceiling, or parallel to the wall, or at anoblique or intermediate angle with respect to the ceiling or wall.

In FIG. 2, we see a schematic view of a light guide 212 with a lightsource such as a discrete light source 214 injecting light into thelight guide, and diffractive surface features 213 coupling guided-modelight 216 out of the light guide to provide out-coupled light 217 a, 217b. The light guide 212, which may be the same as or similar to the lightguide 112 discussed above, has a first major surface 212 a on which thediffractive surface features 213 are provided, a second major surface212 b opposite the first major surface, and a side surface 212 c throughwhich light from the light source 214 can enter the light guide. Thelight source 214 may include an active element 214 a such as one or moreLED dies which convert electricity into visible light, and one or morereflective members 214 b which help direct some of the misdirected lightfrom the element 214 a into the side surface 212 c of the light guide212. Guided-mode light 216 from the light source 214 propagates viatotal internal reflection (TIR) along and within the light guide 212over a range of angles α which may be measured relative to the localplane of the light guide, in this case, the x-y plane. Out-coupled light217 a, 217 b may be measured or characterized, at least in part, by thepolar angle θ between the direction of propagation of a given light ray217 c and an axis 217 d normal to the local plane of the light guide, inthis case, the z-axis. FIG. 2 also shows an incident light beam 218 aimpinging upon and entering the light guide 212 through the majorsurface 212 b, propagating through the light guide 212 asnon-guided-mode light, and exiting the light guide through the majorsurface 212 a as transmitted light beam 218 b. The transmitted beam 218b is preferably minimally deviated by the diffractive surface features213 such that objects can be viewed through the light guide 212 with lowdistortion.

We will now elaborate on relevant design characteristics of thediffractive surface features 213 that allow them to provide some of thefunctional properties discussed above. Typically, the diffractivesurface features 213 are grooves or ridges/prisms with well-definedfaces that follow predetermined paths in plan view. For purposes of FIG.2, we will assume for simplicity that the diffractive features 213follow straight, linear paths that are parallel to each other and to they-axis. This assumption is not as restrictive as it seems, because thestraight, linear features can approximate a very small portion orsection of diffractive surface features that follow curved paths in planview, such as concentric circles or spiral arcs. We also assume forsimplicity that the diffractive features 213 have a uniformcenter-to-center spacing known as “pitch”, which is labeled “p” in FIG.2. This assumption is also not as restrictive as it seems, because theuniformly spaced diffractive features 213 can approximate a very smallportion or section of diffractive surface features whose pitch p changesas a function of position. The diffractive surface features 213 are alsoassumed to have a depth (grooves) or height (prisms) “h” as shown inFIG. 2.

The diffractive surface features 213 with the assumed linearconfiguration and constant pitch can be referred to as a single-pitch(or periodic) one-dimensional (1D) diffraction grating. The single-pitch1D grating is directly coupled to, and forms the major surface 212 a of,the light guide 212, which we assume has a refractive index of n and isimmersed in air or vacuum. Light from the light source 214 of opticalwavelength λ is injected or launched into the light guide 212 throughthe side surface 212 c, and propagates primarily by TIR within and alongthe light guide as guided-mode light 216. When such light impinges uponand interacts with the diffractive surface features 213, a fraction (η)of the guided-mode light 216 is extracted as out-coupled light 217 a,217 b. The out-coupled or extracted light 217 a, 217 b propagates alonga direction that is orthogonal to the light guide surface (e.g. having apolar angle θ=0 in FIG. 2) when the following condition is met:m×(λ/n)=d×cos(α).  (1)In this equation: α refers to the angle at which the guided-mode lightimpinges on the grating surface, measured relative to the plane of thesurface substantially as shown in FIG. 2; m is the diffraction order; nis the refractive index of the light guide 212; λ is the wavelength oflight; and d is the grating pitch, which is labeled “p” in FIG. 2. Forexample, for green light with λ=530 nm launched on-axis (α=0 degrees)into an acrylic light guide having a refractive index n=1.5, the gratingpitch d (or p) should equal 353 nm, and only the first diffraction order(m=1) is possible. For other values of α and λ, the extraction directionwill in general no longer be orthogonal to the light guide surface.

A computer simulation can be used here to illustrate the angulardistribution characteristics of extracted or out-coupled light as afunction of the light source wavelength, for the single-pitch 1Ddiffraction grating. In order to fully characterize the angulardistribution, both polar angle (angle θ in FIG. 2) and azimuthal angle(the angle measured in the x-y plane relative to a fixed direction oraxis in the x-y plane) should be considered. For purposes of thesimulation, for simplicity, we assume: that the light source 214 and thelight guide 212 (including the diffractive surface features 213) extendinfinitely along axes parallel to the y-axis; that the pitch d (or p) is353 nm; and that the light source 214 has a Lambertian distribution inthe x-z plane, i.e., an intensity proportional to the cosine of α, forlight emitted by the light source 214 in air before impinging on theside surface 212 c. After running the simulation with these assumptions,we calculate the total integrated optical power density as a function ofthe polar angle θ for 3 different optical wavelengths λ, and plot theresults in FIG. 3. In that figure, curves 310, 312, 314 show theintegrated optical power density for the optical wavelengths λ of 450 nm(blue light), 530 nm (green light), and 620 nm (red light),respectively.

The simulated results of FIG. 3 demonstrate, among other things, thewavelength-dependent nature of light extraction using diffractivesurface features. Although the curves 310, 312, 314 overlap to someextent, their peak intensities occur at polar angles that differ fromeach other by more than 10 degrees, with the red and blue peaks beingseparated by almost 30 degrees. In this particular example, the peak forgreen light occurs close to θ=0, i.e., along a direction nearlycoincident with the optical axis of the light guide. We can cause thepeak for red light to coincide with the optical axis by increasing thepitch p, and we can cause the peak for blue light to coincide with theoptical axis by decreasing the pitch p.

In addition to the simulation, we also fabricated a single-pitch 1Ddiffraction grating to demonstrate its utility as a light extractor fora light guide. First, a diamond tip for a diamond turning machine (DTM)was shaped using a focused ion beam (FIB) to form a V-shaped diamond tipwith an included angle of 45 degrees. This diamond tip was then used tocut symmetric, equally spaced V-shaped grooves around the circumferenceof a copper roll to make a diffraction grating master tool. Acast-and-cure replication process was then used to transfer the gratingpattern from the master tool to a film substrate. A triacetate cellulose(TAC) film having a thickness of 3 mils (about 76 micrometers) was usedas a base film or substrate due to its low birefringence and itsrefractive index value (n=1.5), which matches well to the refractiveindex of typical light guide materials. This base film was applied tothe master tool with a thin acrylate resin coating therebetween. Theacrylate resin composition comprised acrylate monomers (75% by weightPHOTOMER 6210 available from Cognis and 25% by weight1,6-hexanedioldiacrylate available from Aldrich Chemical Co.) and aphotoinitiator (1% by weight Darocur 1173, Ciba Specialty Chemicals).Ultraviolet light from a mercury vapor lamp (“D” bulb) was used for bothcasting and post-curing the microreplicated resin on the base film. Thecasting roll temperature was set at 130 degrees F. (54 degrees C.), andthe nip pressure was set at 20 to 25 psi (about 138,000 to 172,000pascals).

A microphotograph of the structured or grooved surface of the resultingdiffraction grating film is shown in FIG. 4. The pitch of thediffractive surface features in this figure is about 400 nanometers, andthe depth of the grooves (or height of the prisms) is about 500nanometers.

This film was then laminated to a 2 mm thick acrylic plate, which wasclear, flat, and rectangular, using a layer of optically clear adhesive(3M™ Optically Clear Adhesive 8172 from 3M Company, St. Paul, Minn.)such that the diffraction grating faced away from the acrylic plate andwas exposed to air, and such that no significant air gaps were presentbetween the base film of the diffraction grating film and the flat majorsurface of the acrylic plate to which the film was adhered. Thelaminated construction thus formed a light guide having the single-pitch1D diffraction grating serving as diffractive surface features on onemajor surface of the light guide. The light guide included a flat,straight side surface extending parallel to the groove direction of thediffractive surface features, similar to the configuration of FIG. 2. Alight source was constructed using a linear array of orange-emittingLEDs (obtained from OSRAM Opto Semiconductors GmbH), each LED having acenter wavelength of about 590 nm and a full-width-at-half-maximum(FWHM) bandwidth of about 20 nm. The discrete character of theindividual LEDs was masked by placing a diffuser plate (type DR-50 fromAstra Products Inc., Baldwin, N.Y.) in front of the LEDs, i.e., betweenthe LEDs and the side surface of the light guide, to provideillumination that was more spatially uniform. The light source thusapproximated a linear light source emitting light that was approximatelymonochromatic at a wavelength of 590 nm.

The light source was energized, and the intensity of the out-coupledlight emitted through the diffractive surface features was measured as afunction of polar angle and azimuthal angle using a conoscopic camerasystem. The measured conoscopic intensity distribution is shown in FIG.5. In this figure, the direction of elongation of the light source, andthe groove direction, corresponds to azimuthal values of 0 and 180degrees. The measured intensity or luminance in an orthogonal referenceplane, i.e., in a plane corresponding to azimuthal values of 90 and 270degrees in FIG. 5, is plotted as a function of polar angle θ in FIG. 5a. The reader may note the similarity of the curve in FIG. 5 a relativeto the shape of the curves 310, 312, 314 in FIG. 3. The reader may alsonote in reference to FIG. 5 that light is extracted by the 1Ddiffraction grating in a narrow crescent-shaped distribution that doesnot lie in a plane, but that shifts in azimuthal angle as a function ofpolar angle.

Other aspects of the extended area lighting device discussed inconnection with FIGS. 4, 5, and 5 a include: light is extracted orout-coupled equally from both major surfaces of the light guide (seee.g. surfaces 212 a, 212 b of FIG. 2), which is a result of thesymmetric design of the diffractive surface features (i.e., thesymmetric V-shaped grooves that form the linear diffraction grating); ifthe monochromatic source is replaced with a white light source and/ormulti-colored light sources, angular color separation will occur as aresult of the diffraction phenomenon (see e.g. FIG. 3); no diffusercomponent is needed in the device (although in the embodiment of FIGS. 5and 5 a one is included in the light source to mask the discrete natureof the LED light sources) due to the fact that TIR is relied upon toallow the guided-mode light to propagate along the waveguide, anddiffraction is relied upon to extract or out-couple the light from thelight guide; and the crescent-shaped distribution of out-coupled lightis characterized by a relatively narrow light extraction angle.

Guided-mode light may be extracted or out-coupled preferentially throughone major surface of the light guide rather than the other major surfaceby changing the shape of the diffractive surface features, inparticular, making the shape of the individual features (e.g. prisms)asymmetrical. We demonstrate this in connection with FIGS. 6 and 7. InFIG. 6, a lighting device 610 includes a light guide 612 having a firstmajor surface 612 a and an opposed second major surface 612 b. The firstmajor surface 612 a comprises diffractive surface features 613 in theform of facets which form right-angle prism structures of height “h” andpitch “p”. The device 610 also includes a light source 614 disposedproximate a side surface of the light guide 612 to inject light into thelight guide as guided-mode light, such light propagating generally fromleft to right from the perspective of FIG. 6. A computer simulation ofthe device 610 was performed. In the simulation, for simplicity, theprism structures of the diffractive surface features 613 were assumed tobe equally spaced, and extending linearly along axes parallel to they-axis. The light source was also assumed to extend linearly parallel tothe y-axis, and was assumed to emit polarized light of wavelength λ intoair in a Lambertian distribution in a first reference plane parallel tothe plane of the light guide (see the x-y plane in FIG. 2), this lightthen being refracted at the side surface of the light guide. Thesimulation assumed only one propagation angle of light, α=5 degrees asreferenced in FIG. 2, in a second reference plane (see the x-z plane inFIG. 2) perpendicular to the first reference plane. The refractive indexof the light guide was assumed to be 1.5. The optical wavelength λ andthe grating pitch p were initially selected such that the out-coupledlight was extracted orthogonal to the light guide surface for firstorder diffraction (m=1), which yielded λ≈520 nm and p≈350 nm. Thegrating height h was then varied over a range from 50 to 500 nm, whilethe pitch p was held constant at 350 nm. For each embodiment associatedwith a specific value for the grating height, the following quantitieswere calculated by the computer simulation software:

-   -   extraction efficiency for transverse magnetic (TM) polarized        light extracted from the first major surface 612 a, referred to        here as TM-top extraction efficiency;    -   extraction efficiency for transverse electric (TE) polarized        light extracted from the first major surface 612 a, referred to        here as TE-top extraction efficiency;    -   extraction efficiency for transverse magnetic (TM) polarized        light extracted from the second major surface 612 b, referred to        here as TM-bottom extraction efficiency; and    -   extraction efficiency for transverse electric (TE) polarized        light extracted from the second major surface 612 b, referred to        here as TE-bottom extraction efficiency.        In this regard, “extraction efficiency” refers to the amount        (expressed as a percentage) of specified light (TM or TE)        extracted from the specified major surface (612 a or 612 b) for        a single interaction, divided by the amount of such specified        light propagating within the light guide immediately before the        interaction of the light beam with the extraction surface.

The calculated quantities are plotted in FIG. 7, where curve 710 is theTM-bottom extraction efficiency, curve 712 is the TE-bottom extractionefficiency, curve 714 is the TM-top extraction efficiency, and curve 716is the TE-top extraction efficiency. These results demonstrate thatguided-mode light can be extracted preferentially through one majorsurface of the light guide by making the shape of the individualdiffractive features (e.g. prisms) asymmetrical. The results alsodemonstrate that the degree to which light is preferentially extractedfrom one major surface depends on details of the particular shape of thediffractive features. In the case of right-angle prism features,preferential extraction can be maximized by selecting a height happroximately equal to the pitch p.

The diffractive surface features may be tailored so that light emittedfrom one major surface of the light guide (e.g. out-coupled light 217 ain FIG. 2) is the same as, or similar to, the light emitted from theopposed major surface of the light guide (e.g. out-coupled light 217 bin FIG. 2). The light emitted from the opposed surfaces may be the samewith respect to color, intensity, and/or the angular distribution ofcolor and/or intensity of the out-coupled light. In one approach,diffractive surface features may be provided on both opposed majorsurfaces, and these diffractive surface features may be mirror images ofeach other with respect to a reference plane disposed between andequidistant from the opposed major surfaces, such that the lightingdevice possesses mirror image symmetry with respect to such a referenceplane. In alternative embodiments, the diffractive surface features maybe tailored so that light emitted from one major surface of the lightguide is substantially different from the light emitted from the opposedmajor surface of the light guide. The light emitted from the opposedsurfaces may be different with respect to color, intensity, and/or theangular distribution of color and/or intensity of the out-coupled light.For example, an observer may perceive that light of one color is emittedfrom one major surface, and light of a substantially different color isemitted from the opposed major surface. In a horizontally-mountedlighting device, white light sources may be used with suitably tailoreddiffractive surface features such that white light of a relatively coolcolor temperature (bluish tint) is directed upwards towards the ceiling,and white light of a relatively warmer color temperature (reddish tint)is directed downwards towards the floor, or vice versa.

In applications where the angular separation of different colors oflight due to diffraction is undesirable, several design approaches canbe used to overcome the color separation issue. In one approach, shownin FIG. 8, two or more light guides can be stacked together. In anotherapproach, shown in FIG. 9, different diffractive surface features aredisposed on opposite major surfaces of a given light guide, and tailoredfor different colored light sources. In still another approach, shown inFIGS. 10 and 11, the diffractive surface features on a given majorsurface of a light guide may include groups of surface features ofdifferent pitches. Note that although these approaches are presented inconnection with dealing with the color separation issue, they may alsobe used for other purposes including utilitarian and/or aestheticpurposes in which color separation still occurs, or in single-colorembodiments that employ only light sources of a given desired(non-white) color. Note also that although the various approaches aredescribed individually, any two or more of the approaches can becombined together and used in a single embodiment.

Turning then to FIG. 8, we see there a schematic view of a lightingdevice 810 that includes a plurality of light guides 812, 832, 852 in astacked or layered arrangement. Each light guide has a pair of opposedmajor surfaces, i.e., light guide 812 has major surfaces 812 a, 812 b,light guide 832 has major surfaces 832 a, 832 b, and light guide 852 hasmajor surfaces 852 a, 852 b. At least one major surface of each lightguide preferably includes diffractive surface features, for example,major surface 812 a may include diffractive surface features 813, majorsurface 832 a may include diffractive surface features 833, and majorsurface 852 a may include diffractive surface features 853. The device810 also includes light sources 814 a, 814 b, 834 a, 834 b, 854 a, 854 barranged as shown to inject light into the respective light guides e.g.through their respective side surfaces, so as to provide guided-modelight in the light guides. Preferably, each of the light guides(including their diffractive surface features) has a low opticaldistortion such that non-guided-mode light can pass through the lightguide relatively undisturbed. In this way, light extracted from thelight guide 832 by the diffractive surface features 833 can pass throughthe light guide 812 to reach a user 820 and/or surface 822, and lightextracted from the light guide 852 by the diffractive surface features853 can pass through both light guide 812 and light guide 832 to reachthe user 820 and/or surface 822. The surface 822 may be disposed tointersect the optical axis of the light guides, and may be perpendicularto such optical axis and disposed at a distance D from the light guidesof at least 10 times a characteristic transverse dimension L (e.g. adiameter or length) of the light guides. The characteristic transversedimension L may be a maximum in-plane dimension (caliper measurement) ofthe light guide. Alternatively, the minimum in-plane dimension (calipermeasurement), or the average of the minimum and the maximum, may be usedfor the characteristic dimension L. Preferably, D is at least 2*L but nomore than 50*L. Alternatively or in addition, D may be expressed inabsolute units. Preferably, D is at least 0.2 meters but no more than 15meters. The user 820 may also observe objects such as object 824, whichmay be the same as or similar to object 124 discussed above, through thestack of light guides 812, 832, 852 with little or no opticaldistortion.

If it is desirable to overcome the color separation issue, the variouslight guides, light sources, and diffractive surface features in thedevice 810 may be tailored to provide different colors of out-coupledlight to the user 820 and/or surface 822 so that the sum of all suchlight provides substantially white light illumination. For example, thelight sources 854 a, 854 b may emit red light and the diffractivesurface features 853 may optimally extract such light along an opticalaxis (e.g. an axis parallel to the z-axis) of the device, and the lightsources 834 a, 834 b may emit green light and the diffractive surfacefeatures 833 may optimally extract the green light along the sameoptical axis, and the light sources 814 a, 814 b may emit blue light andthe diffractive surface features 813 may optimally extract the bluelight along the same optical axis. Of course, red, green, and blue inthe order described are merely examples, and the reader will understandthat a multitude of alternative combinations are contemplated.Furthermore, although three light guides are shown in the stack of FIG.8, other numbers of light guides, including two, four, or more, can alsobe used. The constituent components of each layer within the stack mayall have the same or similar design, e.g., the same light guidedimensions and characteristics, the same dimensions and characteristicsof the diffractive surface structures, and the same numbers, colors, andarrangements of LEDs. Alternatively, the constituent components of eachlayer may differ from corresponding components in other layers in any ofthese respects. Similar to lighting device 110, the device 810 mayprovide illumination of a substantially uniform color (which uniformcolor may be substantially white or a different, e.g. non-white, color)on the surface 822, while providing a colored appearance when the user820 looks directly at the device 810. Also, the user may observe spatialpattern(s) such as indicia in the emitting area of the device 810, whichpattern(s) or indicia may originate with any one, or some, or all of thelayers within the stack, and/or one or more bands having a 3-dimensionalappearance in the emitting area of the device 810, which bands mayoriginate with any one, or some, or all of the layers within the stack.

The light guides 812, 832, 852 of FIG. 8 may be mechanically connectedto each other by attachment of the light guides to a framework ofinterconnected support members, e.g., rings or similar structures thatcompletely or partially encircle each of the light guides. Frameworks ofinterconnected support members are discussed further below.

Turning to FIG. 9, we see there a schematic view of a lighting device910 that includes a light guide 912, and light sources 914 a, 914 bdisposed to inject light into different (e.g. orthogonal) side surfacesof the light guide. The light guide 912 has a pair of opposed majorsurfaces 912 a, 912 b. In device 910, each major surface has its owndiffractive surface features: surface 912 a has diffractive surfacefeatures 913 a, and surface 912 b has diffractive surface features 913b. The diffractive surface features are represented only schematicallyin the figure, but indicate that features 913 a extend generallyparallel to one in-plane axis (e.g. the y-axis), and the features 913 bextend generally parallel to an orthogonal in-plane axis (e.g. thex-axis). The light sources are likewise positioned and configured toinject light generally along orthogonal in-plane directions, with source914 a disposed to inject light generally along the x-axis and source 914b disposed to inject light generally along the y-axis. The term“generally” is used here because the light sources need not be (and inmany cases are not) collimated, but emit light in a distribution ofangles in the x-y plane. Also, although the sources 914 a, 914 b areeach shown as a discrete point source such as a single LED emitter, theymay alternatively each be a linear array of such discrete sourcesextending along the respective side surface of the light guide, or alinear or bar-shaped extended source. Nevertheless, light from thesource 914 a propagates predominantly along the in-plane x-axis, suchthat it interacts strongly with the diffractive surface features 913 aand weakly with the diffractive surface features 913 b, and light fromthe source 914 b propagates predominantly along the in-plane y-axis,such that it interacts weakly with the features 913 a and strongly withthe features 913 b.

This selective coupling of the light sources to different respectivediffractive surface features on the light guide using geometry ordirectionality can, if desired, be used to address the color separationissue. For example, the light sources may be substantially complementaryin their emission spectra, e.g., source 914 a may emit blue light andsource 914 b may emit yellow light, in which case the diffractivesurface features 913 a may be configured to extract blue light along agiven direction such as an optical axis (e.g. the positive z-axis) ofthe lighting device 910, while the diffractive surface features 913 bmay be configured to extract yellow light along the same direction, soas to provide substantially white light illumination along the opticalaxis. There is little interaction between the blue or yellow light withthe diffractive surface features (light extraction grating) of theopposite color because, as explained above, the grooves for blue lightextraction extend generally along the light path of the yellow light,the grooves for yellow light extraction extend generally along the lightpath of the blue light. The different colored light beams are thusguided and extracted independently in the same light guide. The combinedvisual effect of the out-coupled blue and yellow light gives rise to asensation of white light to an observer or user. The color renderingindex (CRI) of the white light in this example may however be relativelylow, because the light guide 912 combines only two colors.

The approach shown in FIG. 9 can be extended to numerous otherembodiments, including embodiments that use light sources of othercolors, including combinations of different complementary colors, andcolors that are not complementary, including also colors that may be thesame (e.g. green-emitting light for both sources 914 a and 914 b, orred-emitting light for both sources). Also, a lighting device such asdevice 910 can be combined with other lighting devices of similar ordifferent design, e.g. in a stacked arrangement as described inconnection with FIG. 8. In such a case, each light guide may beconfigured to emit a combination of two distinct colors, and the colorscollectively emitted from the stack may be selected to produce whitelight with a higher CRI, if desired.

Another approach that may be used to address the color separation issueis the approach shown generally in FIGS. 10 and 11. In these figures,light guides 1012, 1112 are shown in which the diffractive surfacefeatures on a given major surface include groups or packets of surfacefeatures of different pitches. The multiple different pitches can beused generally to provide a desired distribution of various wavelengthsof extracted light from the light guide, assuming light of suchwavelengths is injected into the light guide by one or more lightsources (not shown).

As mentioned elsewhere, the light guides disclosed herein may have avariety of different constructions, including a unitary construction, ora layered construction in which two or more components are attached toeach other with no significant intervening air gaps. In this regard, thelight guides 1012, 1112 are shown to have layered constructions, butthey may be readily modified to have a unitary construction if desired.Conversely, light guides shown as being unitary in other figures may bereadily modified to have layered constructions. In reference to FIG. 10,the light guide 1012 includes a relatively thick plate or othersubstrate 1011 a, to which is attached a film made up of a carrier film1011 b on which a prism layer 1011 c has been cast and cured. Thesubstrate 1011 a, carrier film 1011 b, and prism layer 1011 c preferablyhave the same or similar index of refraction, and are preferably allhighly transmissive to visible light, with little or no scattering orabsorption, although in some cases a controlled amount of absorptionand/or scattering may be acceptable or even desirable. In reference toFIG. 11, the light guide 1112 may have a similar construction to lightguide 1012, and thus may include a relatively thick plate or othersubstrate 1111 a, to which is attached a film made up of a carrier film1111 b on which a prism layer 1111 c has been cast and cured.

Attachment of a prismatic or structured surface film to a plate or othersubstrate to provide a layered light guide can be done by any suitabletechnique. For example, attachment can be achieved using a suitableadhesive, such as a light-transmissive pressure sensitive adhesive.Attachment may also be achieved using injection molding processes,including insert injection molding processes. Chemical bonds can also beused for attachment, e.g., when a curable resin is cast and cured on asuitable substrate such as a carrier film. Alternatively, in the case ofunitary constructions, the diffractive surface features can be formed onat least one surface of a unitary substrate such as a film or plate,e.g. by embossing or molding, including for example injection moldingprocesses. Compression molding, extrusion replication, and directcutting are additional techniques that may be used to form thediffractive surface features. Regardless of whether the diffractivestructures are formed on the surface of a film, plate, or othersubstrate, the diffractive surface features may be fabricated using anysuitable technique now known or later developed. Additional methods thatcan be used to make suitable diffractive surface features are discussedin one or more of: WO 2011/088161 (Wolk et al.); US 2012/0098421(Thompson); and US 2012/0099323 (Thompson).

The light guides 1012, 1112 have respective first major surfaces 1012 a,1112 a, and respective second major surfaces 1012 b, 1112 b opposite thefirst surfaces, as well as side surfaces (not shown). Similar to otherlight guides described herein, the first major surfaces 1012 a, 1112 aare configured to have diffractive surface features 1013, 1113,respectively. The surface features may be referred to as grooves orprisms. The grooves/prisms are shown as having an asymmetric 90 degreesawtooth profile in cross section, but other profiles can also be usedas desired including other asymmetric profiles and symmetric (e.g.V-shaped) profiles. In plan view the grooves/prisms may follow pathsthat are straight, curved, or both (e.g. straight in some places andcurved in other places). Significantly, the diffractive surface features1013, 1113 are arranged into groups or packets, the prisms or grooves inany given packet having a uniform pitch but adjacent packets havingdifferent pitches. In some cases, the packets can be arranged inpatterns that repeat across the surface of the light guide, the smallestrepeating group of packets being referred to here as a “set” of packets.For example, light guide 1012 (FIG. 10) has diffractive surface features1013 which are divided into groove or prism packets 1030, 1031, and1032, these packets being arranged in a repeating sequence which definessets 1040. The prisms or grooves in each of packets 1030, 1031, 1032have a uniform pitch, but the pitch in packet 1030 is less than that inpacket 1031, which in turn is less than that in packet 1032. Light guide1112 (FIG. 11) has diffractive surface features 1113 which is dividedinto groove or prism packets 1130, 1131, 1132, 1133, 1134, and 1135.These packets may also be arranged in a repeating sequence to define set1140. The prisms or grooves in each of packets 1130, 1131, 1132, 1133,1134, and 1135 have a uniform pitch, but the pitch gets progressivelylarger as one moves from packet 1130 to packet 1135. Note that althoughdifferent pitches are used in the various packets shown in FIGS. 10 and11, preferably every one of the pitches is in a range suitable forcoupling some visible guided-mode light out of the light guide byprinciples of diffraction.

The width (in-plane transverse dimension) of the packets and the widthof the sets of packets, when the light guide is seen in plan view, maybe small enough so that they are visually imperceptible to the ordinaryobserver. Alternatively, the width of the packets and/or the widths ofthe sets of packets may be large enough so that they are perceptible asindicia or as an aesthetic pattern to the ordinary observer.

Multiple pitch extraction designs such as those depicted in FIGS. 10 and11 can be used for color mixing. Generally speaking, at least twodifferent packets, characterized by two different pitches, can be used,but in many cases at least three different packets, characterized bythree different pitches p1, p2, p3, are desirable. The choice of thepitch dimension is a function of the refractive index (n) of the lightguide, as well as a function of the wavelength of light (λ) we wish toextract from the light guide with the given packet. In an exemplary casewe may select p1=λ1/n, where λ1 is in a range from 400 to 600 nm, andp2=λ2/n, where λ2 is in a range from 500 to 700 nm, and p3=λ3/n, whereλ3 is in a range from 600 to 900 nm. In the case of light guides made ofacrylic (n≈1.49) or similar materials, these conditions correspond to apitch p1 in a range from about 268 to 403 nm, p2 in a range from about336 to 370 nm, and p3 in a range from 403 to 604 nm. Polychromatic lightsuch as white light propagating within the light guide interacts withthe multiple pitch packets so that light of different colors isdiffracted (out-coupled or extracted from the waveguide) at differentangles for each given packet, the extraction angle for any given coloralso being different for the different packets. As a result, light ofthe various colors can be mixed or combined to provide illumination withsubstantial color uniformity, e.g. substantially white light, for usersor objects disposed at a suitable distance from the light guide.

In exemplary embodiments, the lighting device may utilize a plurality oflight sources having different spectral outputs, and a controller can beused to independently control the different light sources to actively ordynamically control the perceived color of the light emitted by thelighting device. This active control can be used to adjust or otherwisechange the color temperature, correlated color temperature, and/or thecolor rendering index (CRI) of the output light. Assemblies orcombinations of red, green, and blue-emitting LEDs (RGB), or red, green,blue, and white-emitting LEDs (RGBW), are of particular benefit for thispurpose. Also, light guides that incorporate a multiple pitch extractiondesign are also of particular benefit. Preferably, the multiple pitchdesign incorporates at least one packet of diffractive features of agiven pitch for each narrow-band emitting light source, e.g., one ormore packets whose pitch is tailored for red light, one or more packetswhose pitch is tailored for green light, one or more packets whose pitchis tailored for blue light, and so forth. Note that individual narrowband colors are not limited to red, green, and blue, and light sourcesthat emit other non-white colors such as yellow or amber may also beused to expand the color gamut of the disclosed lighting devices.

A design parameter of interest for the multi-pitch grating design, aswell as for other disclosed diffractive surface feature designs, is theeffective extraction efficiency. Extraction efficiency was discussedabove and will not be repeated here. The “effective” extractionefficiency refers to the percentage of specified light extracted fromthe specified major surface (612 a or 612 b) upon a single interaction,divided by the amount of such specified light propagating within thelight guide immediately before the interaction with the extractionsurface. The effective extraction efficiency for diffractive surfacefeatures (grooves or prisms) of a given pitch can be evaluated andcompared to the effective extraction efficiencies of other pitches. Ingeneral with given system parameters, the effective extractionefficiency of a given pitch: is a linear function of (i.e., directlyproportional to) the plan-view area coverage of diffractive featureshaving that pitch (e.g., for the smallest pitch in FIG. 10, the sum ofthe plan-view areas of the three packets 1030 on the surface); and alsodepends on other factors including the pitch of the diffractive featuresand the cross-sectional profile shape of the diffractive features(grooves/prisms). If substantial color uniformity is desired, theeffective extraction efficiencies for the different pitches may be madecomparable to each other, e.g., the ratio of effective extractionefficiencies for any two distinct pitches may lie within the range fromabout 0.3 to 3.

As we saw in connection with FIGS. 4, 5, and 5 a, a monochromaticLambertian light source used to inject light into a light guide having asingle pitch linear diffraction grating gives rise to a crescent-shapeddistribution of out-coupled light characterized by a relatively narrowlight extraction angle. If even further angular narrowing of theout-coupled light is desired, the light source can be reconfigured withsuitable lenses, mirrors, or other components to emit light that iscollimated or nearly collimated rather than Lambertian. Conversely, ifangular widening of the out-coupled light is desired, the light sourcecan be reconfigured to emit light over a broader angular range than aLambertian distribution. Microstructured optical films can be combinedwith light sources such as LEDs or lasers to tailor the angular spreadof light injected into the light guide, thereby also affecting theangular spread of the out-coupled light. Suitable microstructuredoptical films are described in PCT Patent Publications WO 2012/075352(Thompson et al.) and WO 2012/075384 (Thompson et al.). These opticalfilms, which may be referred to as uniformity tapes, can be applieddirectly to the edge or side surface of a light guide and compriserefractive structures facing outward toward the light source to enhancecoupling of light into the light guide. The refractive structures mayalternatively be incorporated directly into the side surface orinjection edge of the light guide, e.g. by injection molding, embossing,or direct machining. Such optical films or refractive structures, whendisposed between an LED source and the side surface of a light guide,can broaden the angular spread of light injected into the light guide,and can be used with one, some, or all of the light sources in any ofthe embodiments disclosed herein. Optical films with custom designedreplicated structures can also be used with coherent lasers to provide awell-defined rectangular-shaped angular distribution of light (i.e., alight distribution of approximately constant intensity over a specifiedcone of angles, and zero or near zero intensity outside the specifiedcone) for injection into the light guide.

The angular spread of the out-coupled light can also be tailored byappropriate selection of the physical width (in-plane transversedimension) of the packets of diffractive features, where the physicalwidth is measured orthogonally to the direction of elongation of theprisms/grooves. The physical width of each packet affects all colors oflight interacting with the packet, and the overall extracted light is anaverage effect of all the packets. Physical widths that are small tendto broaden the angular width of the out-coupled light, while physicalwidths that are large tend to narrow the out-coupled light angularwidth. However, the amount of angular broadening or narrowing that canbe achieved by physical width adjustment is somewhat limited becausephysical widths that are too small can lead to excessive light spreadingsuch that the diffractive surface features produce a high degree ofdistortion or scattering, and such that the light guide appears to bediffusive rather than diffractive.

Another technique for producing illumination that is more angularlydispersed (e.g. for better spatial uniformity at remote surfaces) is touse a pattern of diffractive surface features oriented along differentin-plane directions, e.g., corresponding to different azimuthal anglesin the conoscopic plot of FIG. 5. The differently oriented diffractivefeatures can then be combined with corresponding light sources that emitlight generally along different in-plane directions tailored for maximumextraction efficiency with the corresponding diffractive features. Thecombination of the variously oriented diffractive features and thevariously oriented light sources can produce out-coupled light emittedat a variety of azimuthal directions, resulting in illumination that ismore angularly dispersed and more spatially uniform. In an exemplaryembodiment, at least three distinct diffractive feature orientations canbe used, corresponding to in-plane axes separated from each other byazimuthal angles of 120 degrees.

Differently oriented diffractive features can also be achieved throughthe use of continuously curved grooves or prisms, e.g., grooves orprisms that are circular, oval, or elliptical in shape (in plan view),or portions of such shapes, e.g., arcs, including series ofinterconnected arcs such as in sinusoidal or otherwise undulatingshapes. In that regard, embodiments disclosed herein that are describedas having linear diffractive surface features can alternatively employdiffractive features that are curved. Linear or curved diffractivesurface features, when combined with discrete light sources and/ornon-uniform reflective structures, can be used to produce visualfeatures in the form of bright or dark bands. Bands such as these arehighly undesirable in most extended source applications, but in somecases can be exploited to provide the lighting device with an aesthetic3-dimensional appearance.

FIG. 12 shows an exemplary light guide 1212 that can be used as acomponent in the lighting devices disclosed herein. The light guide 1212has opposed major surfaces and a side surface 1212 c extendingcontinuously around the periphery of the light guide in the form of anarrow circular ring. Diffractive surface features 1213 are provided onone of the major surfaces. In this embodiment, the diffractive features1213 form a tightly wound spiral, substantially filling one majorsurface of the light guide. The diffractive features 1213 are thus allcurved in plan view over substantially their entire lengths, and thecurvature changes monotonically as a function of radial distance fromthe geometrical center of the light guide 1212 and of the diffractivefeatures 1213, which center is labeled “C” in FIG. 12. A portion of thelight guide 1212 and of the diffractive surface features 1213 is shownin a schematic magnified view in FIG. 12 a. The pitch of the diffractivefeatures (radial distance between adjacent grooves or prisms) can beuniform or non-uniform, as discussed elsewhere herein. In alternativeembodiments, the tightly wound spiral can be replaced with concentriccircles or other similar shapes. In other alternative embodiments, thecircular shape of the light guide 1212 and the substantially circularshape of the diffractive surface features 1213 can be changed to othercurved shapes, such as ellipses or ovals. Furthermore, diffractivesurface features may alternatively be provided on both major surfaces ofthe light guide 1212, or on only a portion of one, or both, majorsurfaces.

Turning now to FIG. 13, shown there is an exemplary arrangement of howdiscrete light sources can be mounted along a curved side surface of alight guide. A lighting device 1310 includes a light guide 1312,discrete light sources 1314 a, 1314 b disposed to inject light into acurved side surface of the light guide 1312, and support structure 1302such as a mounting ring. Diffractive surface features, not shown herebut described elsewhere herein, are provided on a major surface of thelight guide 1312 to extract guided-mode light out of the light guide.The light sources 1314 a, 1314 b may be or comprise LEDs or similarsmall area light sources. The light sources are mounted in apertures orslots of the support structure 1302. If desired, the support structure1302 can be made of a metal or other reflective material to provide anextended reflector along the side surface of the light guide 1312.Alternatively, a thin reflective film 1304 may be interposed between thesupport structure and the side surface. In other embodiments, thesupport structure 1302 can be made of an absorbing (or other lowreflectivity) material, and/or the film 1304 can be made to be absorbingor of low reflectivity. The light sources need not be mounted at theside surface of the light guide in order to provide guided-mode light.For example, the light sources may inject light through an outer (e.g.annular) portion of the major surface of the light guide rather thanthrough the side surface, and the side surface may in that case bebeveled or angled (e.g. at 45 degrees) so that light from the lightsource that enters through the major surface is reflected sideways toprovide guided-mode light.

The support structure 1302 may be part of a framework of interconnectedsupport members which collectively attach to the light guide 1312 andone or more other light guides as disclosed herein to provide a lightingdevice having multiple light guides.

FIG. 14 depicts another light guide 1412 that may be used in thedisclosed light sources. The light guide 1412 is assumed to be flat,lying in an x-y plane, with opposed major surfaces that aresector-shaped or pie-piece-shaped. Bounding the major surfaces are sidesurfaces 1412 c 1, 1412 c 2, 1412 c 3. The side surface 1412 c 1 iscurved, e.g. like an arc of a circle, and the side surfaces 1412 c 2 and1412 c 3 are flat. The side surfaces 1412 c 2, 1412 c 3 intersect at acenter point C, which may be a center of curvature of the curved sidesurface 1412 c 1. Diffractive surface features 1413 are provided on oneor both major surfaces of the light guide 1412. Rather than beingconcentric, the diffractive features 1413 are assumed to all have thesame curvature, which may be equal to the curvature of the curved sidesurface 1412 c 1. Furthermore, the diffractive surface features 1413 arearranged into packets of different pitches. These include: packets a1and a2, having a pitch configured to extract red guided-mode light at apredetermined angle (e.g. orthogonal to the surface of the light guide);packets b1 and b2, having a pitch configured to extract greenguided-mode light at the same or different predetermined angle; andpackets c1 and c2, having a pitch configured to extract blue guided-modelight at the same or different predetermined angle. The packets are thusarranged into two sets of packets.

In an exemplary embodiment, the packets a1, a2 occupy a first total areaof the light guide, the packets b1, b2 occupy a second total area of thelight guide, and the packets c1, c2 occupy a third total area of thelight guide, and the first, second, and third total areas have relativeproportions are related to a spectral intensity distribution of the oneor more light sources. For example, the first total area may be greaterthan the second total area, which may in turn be greater than the thirdtotal area, such that the combination of all red, green, and blue lightextracted from the light guide 1412 in a particular direction, e.g.along an optical axis (see the z-axis in FIG. 14) provides substantiallywhite light illumination at a reference surface of interest that isremote from the light guide 1412. The maximum transverse dimension ofthe light guide 1412 is the radial distance from the center point C tothe side surface 1412 c 1. The reference surface of interest may beperpendicular to the optical axis, and separated from the light guide1412 by a distance D of intermediate length along the optical axis. Thedistance D may be expressed in terms of a characteristic transversedimension L of the first major surface of the light guide, such as theradial distance from the point C to the surface 1412C1. Alternatively,the minimum in-plane dimension (caliper measurement) or the average ofthe minimum and the maximum may be used for the characteristic dimensionL. Preferably, D is at least 2*L but no more than 50*L. Alternatively orin addition, D may be expressed in absolute units. Preferably, D is atleast 0.2 meters but no more than 15 meters.

The reader will appreciate that numerous modifications can be made tothe light guide 1412 in accordance with the other teachings herein. Forexample, other pitch configurations can be used for the diffractivesurface features, including constant pitch over the entire light guide,and other numbers of packet types and/or other numbers of packet sets.Also, the diffractive surface features 1413 may all be made to beconcentric, e.g. with a center of curvature at the center point C,rather than a constant curvature.

FIGS. 15 a and 15 b are schematic views of a lighting device 1510 thathas a substantially colorful appearance when observed by an ordinaryuser 1520, but that provides illumination of a substantially uniformcolor, and which may be substantially white, at a remote referencesurface of interest 1522. The device 1510 includes a light guide 1512having a symmetry or optical axis 1501, which in this case is parallelto the z-axis because the light guide 1512 extends parallel to the x-yplane. The light guide has a characteristic transverse (in-plane)dimension L. The light guide 1512 may be the same as or similar to otherlight guides discussed herein. One or more light sources, represented bylight source 1514, are disposed to inject light into the light guide1512. The light source 1514 preferably emits light throughout thevisible wavelength spectrum, at least, for example, in the red, green,and blue regions of the spectrum. This light enters the light guide andpropagates within and along the light guide as guided-mode light.

A plurality of diffractive surface features, which are not shown in FIG.15 a but are as described elsewhere herein, are provided on at least onemajor surface of the light guide 1512. The diffractive surface featurescouple the guided-mode light out of the light guide 1512 by themechanism of diffraction, such that light of different wavelengths isextracted or out-coupled from the light guide at different angles at anygiven point on the major surface of the light guide. Due to thediffractive effect, an ordinary user 1520 of the device, such as anoccupant of a room illuminated by the device 1510, observessubstantially different colors in different regions of the light guide.For example, as shown in the figure, the user 1520 may perceive light ofa blue color at a position or region A of the light guide, light of atgreen color at a position or region B of the light guide, and light of ared color at a position or region C of the light guide. In general, theperceived colors and their spatial distribution across the output of thelight guide change as a function of viewing direction and viewingposition. The user may observe such colors over a wide range of viewingdirections and at a variety of observation positions, including bothpositions that are relatively close to and positions that are remotefrom the light guide 1512. The observation positions may, for example,be separated from the light guide 1512 by up to about 50 times thedimension L, or as little as 2 times L. The observation positions mayalso or alternatively be separated from the light guide by up to 15meters or as little as 0.2 meters. However, at at least one viewinggeometry, the user observes substantially different colors in differentregions of the light guide. Colors that are “substantially different”may be quantified in terms of the CIE chromaticity diagram, as discussedin patent application publication US 2014/0043847 (Yang et al.).

The diffractive surface features may be tailored, in combination withother elements of the lighting device 1510 such as the output spectrumof the light source 1514, so that the light guide 1512 illuminates areference surface of interest disposed remotely from the light guidewith light that is substantially spatially uniform in color, and that inexemplary embodiments is also substantially white. In FIG. 15 b, such areference surface of interest 1522 is shown to replace the user 1520 atthe same remote observation or illumination position. This position isshown to be offset from the optical axis 1501, but it may alternativelybe in alignment with (lie on) the optical axis. The substantiallyuniform color illumination may defined over a measurement portion of thesurface 1522, the measurement portion defined by the illuminance of thelight on the surface 1522 being above a given threshold value, e.g.,equal to or greater than the maximum illuminance (“Imax”) on the surface1522 divided by the mathematical constant “e”. Within this measurementportion, colors may be said to be “substantially uniform” by referenceto the CIE chromaticity diagram. Such uniform color illumination may bemaintained over the entire measurement portion of the reference surface1522.

To achieve results such as these, the diffractive surface featuresinclude diffractive surface features of different pitches. For example,one or more first packets of first diffractive surface features having afirst pitch, one or more second packets of second diffractive surfacefeatures having a second pitch different from the first pitch, and oneor more third packets of third diffractive surface features having athird pitch different from the first and second pitches, may beincluded. The first, second, and third pitches may be tailored toextract blue light, green light, and red light respectively along adesired observation direction, e.g., parallel to the optical axis 1501.The first, second, and third packets may be arranged in repeating groupsor sets on the major surface of the light guide 1512. The first packetsmay occupy a first total area of the light guide, the second packets mayoccupy a second total area of the light guide, and the third packets mayoccupy a third total area of the light guide, and relative proportionsof the first, second, and third total areas may be related to a spectralintensity distribution of the light source 1514 used for lightinjection. The first, second, and third diffractive surface features mayinclude surface features that, in plan view, extend along a plurality ofin-plane directions. For example, such surface features may besubstantially circular or at least curved in shape, in plan view.

FIGS. 16 and 17 schematically illustrate the concept of tailoring thetotal areas of different types of diffractive surface features such thattheir relative values are related to the spectral intensity distributionof the light source(s) that injects light into the light guide. In FIG.16, a lighting device 1610 includes a light guide 1612 and one or morelight sources disposed to inject light into the light guide, all ofthese light sources represented schematically by a single light source1614. The light guide 1612 has a first major surface 1612 a and anopposed second major surface 1612 b, and at least one of the majorsurfaces is provided with diffractive surface features 1613. Thediffractive surface features 1613 are made up of three different typesof diffractive surface features, the three types differing in groove orprism pitch. First diffractive surface features lie in a region 1630,and are assumed to have a first pitch and other design characteristicstailored to extract blue light from the light guide 1612 along aparticular direction, e.g. parallel to an optical axis of the lightguide. In FIG. 16, the optical axis of the light guide 1612 is parallelto the z-axis. Second and third diffractive surface features lie inregions 1631 and 1632, respectively, and are assumed to have respectivesecond and third pitches tailored to extract green and red light fromthe light guide 1612 along the same particular direction. The regions1630, 1631, 1632 are assumed to occupy first, second, and third totalareas respectively of the surface 1612 a in plan view, the total areasbeing in proportion to the lengths (or widths) of the regions shown inthe figure. For simplicity, FIG. 16 shows each of the first, second, andthird diffractive surface features grouped into a single packet ofdiffractive surface features, the different packets bordering each otherbut not overlapping. In alternative embodiments, each of the varioustypes of diffractive surface features can be divided into numerouspackets of uniform or non-uniform width as desired while preserving thetotal areas occupied by the respective types of diffractive features,and the packets for the different types of diffractive features can beinterspersed on the major surface e.g. in a cyclic, repeating,non-overlapping fashion.

The light source 1614 is assumed to emit light over enough of thevisible spectrum so that its overall output is substantially white(although in some cases the overall output may not be substantiallywhite but nevertheless broadband in character, so that the user canobserve substantially different colors at different regions of the lightguide), but the spectral content need not be uniform or smoothly varyingas a function of wavelength. In fact, we assume that source 1614 emitslight in a substantially non-uniform fashion over the visible spectrum,as indicated schematically by the spectral intensity distribution 1614a. The distribution 1614 a is assumed to have a spike or excess of lightoutput in the blue region of the spectrum relative to the green and redregions. Such a spike may occur with some LED products that use a blueLED die to excite a yellow phosphor. Whatever the cause, the regions1630, 1631, 1632 are tailored to compensate for the blue spike by havingthe first total area substantially less than the second or third totalareas. The smaller total area for region 1630 results in less blue lightbeing extracted along the particular direction (such as the opticalaxis) compared to green or red light. In this way, the extracted lightemitted along the particular direction does not exhibit the same bluespike that is present in the light emitted by the light source 1614 andin the guided-mode light. This allows the lighting device 1610 toilluminate the reference surface of interest disposed remotely from thelight guide with light that is substantially uniform in color. Thesubstantially uniform color may be maintained over a measurement portionof the reference surface defined by the illuminance of the light beingabove a given threshold value, e.g., Imax/e.

FIG. 17 is provided as a contrast to FIG. 16. In FIG. 17, a lightingdevice 1710 includes a light guide 1712 with major surfaces 1712 a, 1712b, diffractive surface features 1713, and light source 1714 disposed toinject light into the light guide. The diffractive surface features 1713are made up of three different types of diffractive surface features ofdiffering pitches: first diffractive surface features in a region 1730,second diffractive surface features in a region 1731, and thirddiffractive surface features in a region 1732. These various componentsof lighting device 1710 may be substantially the same as correspondingcomponents of lighting device 1610 (e.g., the first, second, and thirddiffractive surface features have different first, second, and thirdpitches designed to extract blue, green, and red light respectivelyalong the same particular direction such as the optical axis), exceptthat the spectral intensity distribution 1714 a of the light source 1714is more evenly distributed with regard to the red, green, and blueregions of the visible spectrum than the distribution 1614 a. Thisdifference in spectral output of the light source is compensated for byreadjustment of the first, second, and third total areas. As a result,the first total area is no longer substantially less than the second orthird total areas. In lighting device 1710, the first, second, and thirdtotal areas are more nearly equal to each other. In this way, thelighting device 1710 is able to illuminate a reference surface ofinterest disposed remotely from the light guide with substantially whiteand uniform light, similar to the illumination provided by lightingdevice 1610.

In another variation of FIGS. 16 and 17, the light sources used in thelighting device may be selected from the group of discrete red, green,and blue emitting LEDs. By selecting an appropriate number of each ofthese three LED types, a desired proportion of these three colors can beinjected into the light guide, and the first, second, and third totalareas of the different diffractive surface features can then be tailoredaccordingly so as to provide substantially white light illumination.FIG. 17 a is a schematic representation of the output spectrum of acollection of red, green, and blue LEDs in which the intensity in eachof these three color bands is about equal. In such case, the first,second, and third total areas may be tailored to be approximately equal.

The disclosed lighting devices, which generally include an extendedlight guide and diffractive surface features disposed on at least onemajor surface of the light guide to extract guided-mode light, may alsobe made to include other design elements that work synergistically withthe diffractive surface features. One such design element is a patternedlow index subsurface layer within the light guide. The patternedsubsurface layer may be patterned in a way that is the same as, similarto, or different from the patterning of the other patterned layers orfilms that are incorporated into the lighting device. But unlike suchother patterned layers or films, the subsurface layer is disposedbeneath (although typically close to) the major surface of the lightguide containing the diffractive surface features. The subsurface layeris thus disposed in an interior of the light guide between the opposedmajor surfaces thereof, and the light guide has a non-unitaryconstruction. The subsurface layer functions to selectively block someguided mode light from reaching the diffractive surface features. Thisis accomplished by tailoring the subsurface layer to have first layerportions characterized by a lower refractive index than the bulk of thelight guide, such that some of the guided mode light propagating in thebulk of the light guide is reflected by total internal reflection (TIR)at the first portions and prevented from reaching the diffractivesurface features. The first layer portions reside in first regions ofthe light guide but not second regions thereof, the first and secondregions being coplanar and in some cases complementary. The first andsecond regions may define a pattern that is regular, irregular, random,semi-random, or of any desired design.

In some cases, the subsurface layer is partially continuous with respectto the first and second regions. For example, a nanovoided polymericmaterial may be present in the first layer portions (in the firstregions), and the subsurface layer may also include second layerportions in which the same nanovoided polymeric material is alsopresent, the second layer portions residing in the second regions. Thenanovoided polymeric material may then extend continuously from anygiven first layer portion to any and all second layer portions that areadjacent to such first layer portion. The nanovoided polymeric materialmay provide the first portions of the subsurface layer with a refractiveindex that is substantially lower than the bulk of the light guide. Forexample, the refractive index of the first portions at visiblewavelengths may be less than 1.4, or less than 1.3, or less than 1.2.The nanovoided polymeric material may have a void volume in a range fromabout 10 to about 60%, or from about 20 to about 60%, or from about 30to about 60%, or from about 40 to about 60%. The second layer portionsof the subsurface layer may be composed of the nanovoided polymericmaterial and an additional material.

The additional material may occupy at least a portion of the void volume(and in some cases may substantially completely fill the interconnectednanovoids such that little or no void volume remains), and preferablyhas the effect of changing the refractive index of the second layerportions by at least about 0.03, e.g., from about 0.03 to about 0.5,from about 0.05 to about 0.5, or from about 0.05 to about 0.25, relativeto the first layer portions in which the additional material is notsubstantially present. In some cases the additional material may be thesame material as a binder used to form the nanovoided polymericmaterial. Further information regarding suitable subsurface layershaving the continuous nanovoided polymeric material construction can befound in the following commonly assigned PCT publications, in which thesubsurface layer is referred to as a variable index light extractionlayer: WO 2012/116129 (Schaffer et al.), “Front-Lit Reflective Display”;WO 2012/116199 (Thompson et al.), “Variable Index Light Extraction Layerand Method of Illuminating With Same”; WO 2012/116215 (Schaffer et al.),“Illumination Article and Device for Front-Lighting ReflectiveScattering Element”; and WO 2012/158414 (Thompson et al.), “Back-LitTransmissive Display Having Variable Index Light Extraction Layer”.

In some cases, the subsurface layer is discontinuous with respect to thefirst and second regions. For example, the first layer portions (in thefirst regions) may be printed with a first material of relatively lowrefractive index, and the second regions may be filled with a secondmaterial of relatively high refractive index, e.g., having a refractiveindex substantially matching, or exceeding, that of the bulk of thelight guide. Here, unlike the partially continuous subsurface layerdescribed above, the second material in the second regions may have nocommon structure or composition relative to the first material in thefirst regions, and the subsurface layer may consist essentially of thefirst layer portions.

Exemplary embodiments that incorporate such subsurface layers are shownschematically in FIGS. 18 and 19. In FIG. 18, a light guide 1812includes opposed first and second major surfaces 1812 a, 1812 b, anddiffractive surface features 1813 are formed on the first major surface1812. An optional patterned light transmissive layer 1821, comprising atleast portion 1821 a, is provided atop the major surface 1812 a. Thelight guide 1812, diffractive surface features 1813, and patterned layer1821 may be the same as or similar to corresponding elements describedelsewhere herein. The diffractive surface features 1813 may be providedby a microreplicated optical film 1811 c having a prism layer cast andcured on a carrier film. A major portion or bulk of the light guide 1812may be provided by a plate or other relatively thick substrate 1811 a,to which the microreplicated optical film 1811 c is attached indirectlythrough a subsurface film 1811 b. In the embodiment of FIG. 18, thesubsurface film 1811 b includes a carrier film on which is disposed apatterned low index subsurface layer 1803. The subsurface layer 1803comprises first layer portions 1803 a in first regions 1840, and secondlayer portions 1803 b in second regions 1830. Adhesive layers (notshown) may also be provided between the microreplicated optical film1811 c and the subsurface film 1811 b, and between the subsurface film1811 b and the substrate 1811 a, for reliable and robust attachment withno significant air gaps. Such adhesive layers, and the second layerportions 1803 b, and the carrier films, and the prism layer allpreferably have relatively high refractive indices that match,substantially match, or exceed the refractive index of the substrate1811 a, such that these components support the propagation ofguided-mode light along the light guide 1812 between the surfaces 1812a, 1812 b.

The first layer portions 1803 a of the subsurface layer 1803 comprise asuitable nanovoided polymeric material having a first refractive indexthat is substantially lower than that of the other components of thelight guide 1812. The nanovoided polymeric material may be or compriseany of the ultra low index (ULI) materials discussed elsewhere herein.Preferably, substantially all of each first layer portion 1803 aincludes the nanovoided polymeric material. Further, the index ofrefraction is preferably relatively spatially uniform within each firstlayer portion 1803 a, e.g., the refractive index may change by no morethan ±0.02 across a continuous transverse plane for each layer portion.The refractive index of the first portions 1803 a may be less than 1.4,or less than 1.3, or less than 1.2. The nanovoided polymeric materialmay have a void volume in a range from about 10 to about 60%, or fromabout 20 to about 60%, or from about 30 to about 60%, or from about 40to about 60%.

The second layer portions 1803 b in the second regions 1830 comprise thesame nanovoided polymeric material used in the first layer portions 1803a, but the second portions 1803 b also include an additional material.The additional material, which may permeate some or substantially all ofthe void volume of the nanovoided material, causes the second portions1803 b to have a second refractive index that is different from thefirst refractive index by at least about 0.03, e.g., from about 0.03 toabout 0.5, from about 0.05 to about 0.5, or from about 0.05 to about0.25. The index of refraction is preferably relatively spatially uniformwithin each second layer portion 1803 b, e.g., the refractive index maychange by no more than ±0.02 across a continuous transverse plane foreach layer portion.

As a result of the lower refractive index in the first regions 1840,guided-mode light (sometimes also referred to as supercritical light)that encounters the first layer portions 1803 a is reflected by TIR backtowards the major surface 1812 b before it reaches the major surface1812 a with the diffractive surface features 1813. That is, the firstlayer portions 1803 a deflect or block some of the guided-mode lightfrom reaching and interacting with the diffractive surface features inthe first regions 1840. This is depicted in FIG. 18 by guided-mode lightray 1816 b. On the other hand, the substantial matching (or exceeding)of the refractive index of the second layer portions 1803 b with thoseof the polymers, carrier films, and substrate 1811 a, causes guided-modelight that encounters the second layer portions 1803 b to continuepropagating substantially undisturbed to the first major surface 1812 a,where at least some of the light is extracted or out-coupled into thesurrounding medium, as described in detail above, by the diffractivesurface features 1813. This is depicted in FIG. 18 by guided-mode lightray 1816 a. The subsurface layer 1803 thus selectively, in apattern-wise fashion, deflects some of the guided-mode light within thelight guide 1812 so that it does not interact with the diffractivesurface features 1813.

FIG. 18 a shows a schematic cross section of an exemplary embodiment ofthe patterned low index subsurface layer 1803. The layer 1803 includesfirst layer portions in first regions 1840, the layer portions in bothsuch regions comprising a nanovoided polymeric material. In someembodiments, the nanovoided polymeric material comprises a plurality ofinterconnected nanovoids as described for example in WO 2010/120422(Kolb et al.) and WO 2010/120468 (Kolb et al.). The plurality ofinterconnected nanovoids is a network of nanovoids dispersed in a binderwherein at least some of the nanovoids are connected to one another viahollow tunnels or hollow tunnel-like passages. The nanovoids or pores insuch nanovoided polymeric material can extend to one or more surfaces ofthe material.

The subsurface layer 1803 also includes a second layer portion in asecond region 1830 disposed between first regions 1840. The secondregion comprises the nanovoided polymeric material and an additionalmaterial. This additional material may occupy at least a portion of thevoid volume of the nanovoided polymeric material. The dashed lines inFIG. 18 a are used to indicate general location of the first and secondregions, however, these dashed lines are not meant to describe any sortof boundary between the regions.

In some embodiments, a seal layer is disposed on the patterned low indexsubsurface layer in order to minimize penetration of contaminants intothe latter. For example, a seal layer may be disposed on the patternedlow index subsurface layer such that it is in between the patterned lowindex subsurface layer and an adhesive layer. For another example, aseal layer may be disposed on the patterned low index subsurface layersuch that it is in between the patterned low index subsurface layer andthe substrate or other constituent layer of the lightguide, and the seallayer may have a refractive index that is approximately equal to orgreater than that of the substrate or other layer. Suitable seal layersare discussed in the commonly assigned U.S. patent applications citedabove.

In FIG. 19, a light guide 1912 includes opposed first and second majorsurfaces 1912 a, 1912 b, and diffractive surface features 1913 areformed on the first major surface 1912. An optional patterned lighttransmissive layer 1921, comprising at least portion 1921 a, is providedatop the major surface 1912 a. The light guide 1912, diffractive surfacefeatures 1913, and patterned layer 1921 may be the same as or similar tocorresponding elements described elsewhere herein. The diffractivesurface features 1913 may be provided by a prism layer 1911 c which iscast-and-cured, microreplicated, embossed, etched, or otherwise formedon a high index resin layer 1911 b. The resin layer 1911 b may in turnbe applied to a plate or other relatively thick substrate 1911 a, whichmay comprise a major portion or bulk of the light guide 1912. However,before the resin layer 1911 b is applied to the substrate 1911 a andcured, a patterned low index subsurface layer 1903 is pattern-wiseapplied to the substrate 1911 a. The subsurface layer 1903 comprisesfirst layer portions 1903 a in first regions 1940, but the subsurfacelayer 1903 is either not applied to, or is applied to and later removedfrom, the substrate 1911 a in second regions 1930. Thus, at the time ofapplication of the resin layer 1911 b, the resin layer fills in thespaces in the second regions 1930. If desired, adhesive layers (notshown) and carrier films (not shown) may also be included in theconstruction, depending on the details of manufacture. Any such adhesivelayers and carrier films, as well as the resin layer 1911 b and theprism layer 1911 c, all preferably have relatively high refractiveindices that match, substantially match, or exceed the refractive indexof the substrate 1911 a, such that these components support thepropagation of guided-mode light along the light guide 1912 between thesurfaces 1912 a, 1912 b.

The first layer portions 1903 a of the subsurface layer 1903 arecomposed of a low index material having a first refractive index that issubstantially lower than that of the other components of the light guide1912. In some cases, the low index material may be or comprise ananovoided material such as those discussed in connection with FIGS. 18and 18 a, e.g., a ULI material. In other cases, the low index materialmay be an optical material that is not nanovoided, e.g., a UV curableresin comprising at least one fluorinated monomer, at least onefluorinated oligomer, at least one fluorinated polymer, or anycombination of such fluorinated materials. Preferably, the refractiveindex of the first portions 1903 a is less than 1.47, or less than 1.43,or less than 1.4, or less than 1.3, or less than 1.2.

The high index resin layer 1911 b may be composed of any suitablepolymer or other light-transmissive material having a suitably highrefractive index so that a substantial amount of guided-mode light canpropagate from the substrate 1911 a to the prism layer 1911 c.

As a result of the lower refractive index in the first regions 1940,guided-mode or supercritical light that encounters the first layerportions 1903 a is reflected by TIR back towards the major surface 1912b before it reaches the major surface 1912 a with the diffractivesurface features 1913. That is, the first layer portions 1903 a blocksome of the guided-mode light from reaching and interacting with thediffractive surface features in the first regions 1940. This is depictedin FIG. 19 by guided-mode light ray 1916 b. On the other hand, thesubstantial matching (or exceeding) of the refractive index of the resinlayer 1911 b with those of the polymers, carrier films, and substrate1911 a, causes guided-mode light that encounters the second regions 1930to continue propagating substantially undisturbed to the first majorsurface 1912 a, where at least some of the light is extracted orout-coupled into the surrounding medium, as described in detail above,by the diffractive surface features 1713. This is depicted in FIG. 19 byguided-mode light ray 1916 a.

The pattern provided by the patterned low index subsurface layer (e.g.,layers 1803, 1903) may be closely related, loosely related, or notrelated at all to the pattern provided by the patterned lighttransmissive layer (e.g., layers 1821 and 1921). In some cases, thesubsurface pattern may be a gradient pattern designed to deliver uniformlight or luminance to the diffractive surface features on the majorsurface of the light guide. In such cases, the printed pattern (ifpresent) on the diffractive surface features can be any desired shape orimage, and no registration of any kind between the two patterns isneeded. Typically, the two patterns would at least partially overlap insuch cases. In other cases, the subsurface pattern may be in the form ofa specific image (e.g. indicia), whether a solid image print or ditheredprint in the shape of an image. In these cases, the printed pattern (ifpresent) on the diffractive surface features may be registered with thesubsurface pattern, but such registration is not required. For example,in some cases, for aesthetic or artistic purposes, distinctly differentimages with no particular alignment or registration can be provided bythe two patterns. Such patterns, which would typically be at leastpartially overlapping, can be used to create interesting levels ofcontrast in the illumination scheme to provide a unique appearance forthe lighting device. However, in some cases, alignment or registrationof the two patterns can be used to amplify the visual effect or contrastof foreground and background areas of the patterns, e.g., by selectivelydelivering more light to printed areas of the diffractive surfacefeatures and blocking light from reaching non-printed areas of thediffractive surface features, or vice versa. In that regard, thepatterns can be made to be spatially complementary, and registered toeach other such that the subsurface pattern delivers light substantiallyonly to non-printed regions of the diffractive surface features, whichmay also result in a contrast enhancement of the image. In still othercases, the two patterns may be the same or similar to each other, butoffset in registration by a controlled amount to provide a shadowingeffect, such as the shadowing effect used for displayed text commonlyused in computer presentation software.

In addition to being useful as luminaires for illuminating work spaces,living areas, and the like, lighting devices such as those shown anddescribed in FIGS. 18 and 19, as well as other lighting devicesdisclosed herein (particularly ones that incorporate only one lightguide), may alternatively be useful as illuminated security features,wherein the pattern(s) provided by the printed layer(s) provide indiciathat may be covert and/or overt in nature as desired. In some securityapplications, the device may be incorporated into or applied to aproduct, package, or document, e.g. as an indicator of authenticitysince the visual features are difficult to copy or counterfeit. Suchsecurity applications may include: cards of various types includingidentification cards, social security cards, health cards, insurancecards, business cards, membership cards, voter registration cards, phonecards, stored value cards, gift cards, border crossing cards,immigration cards, and financial transaction cards (including creditcards and debit cards); badges; passports; drivers licenses; vehiclelicense plates; gun permits and other permits; event passes; advertisingpromotions; product tags including hang-tags; product packaging; labels;charts; maps; and other security articles and documents.

In some cases, such as in a card, one or more miniature light sourcessuch as LEDs may be included in the construction at or near an edge ofthe card to provide the guided-mode light. In other cases, such as inthe case of a passport or other security document, but also in the caseof cards, light sources may not be included in the article itself, butthe article may be configured for use with a reader or similar testingdevice that contains one or more suitable light sources adapted tocouple to an edge (or other surface) of the card or document to injectlight into the light-transmissive layer or layers that make up the lightguide, or the article may be configured for use with natural lightsources. The light guide may be relatively thick and rigid, as in thecase of a clear light-transmissive financial transaction card, orrelatively thinner and flexible, as in the case of a polymer sheet foruse in a passport, for example.

An embodiment that may be useful as a luminaire to provide generalpurpose or decorative illumination

In the discussion near the beginning of this detailed description, wesay we have found that unique lighting devices can be made by combiningan extended area light guide with other components or features. One suchother component or feature is one or more light sources configured toproject light through the light guide as non-guided-mode light. Alighting device that makes use of this combination is shown in FIG. 20.In this figure, lighting device 2010 may be the same as or similar tolighting device 110 of FIG. 1, where the object 124 is a spotlight,light bulb, LED, or other light source that (in some cases) may have nodiffractive surface features, but that is mounted such that most or atleast some of the light it emits is directed through the light guide asnon-guided-mode light. Lighting device 2010 thus includes discrete lightsources 2014 a, 2014 b, and an extended area light guide 2012 whichincludes opposed major surfaces 2012 a, 2012 b, side surfaces, anddiffractive surface features 2013 provided on major surface 2012 a,which couple guided-mode light 2016 out of the light guide as emittedlight 2017 a, propagating generally towards a reference surface ofinterest 2022, and as emitted light 2017 b, propagating generally awayfrom the reference surface 2022. The light sources 2014 a, 2014 b, lightguide 2012, and diffractive surface features 2013 may be the same as orsimilar to corresponding elements of lighting device 110.

The light guide 2012 and its diffractive surface features 2013 aredesigned such that the light guide 2012 provides little or no opticaldistortion for non-guided-mode light. In the lighting device 2010, thenon-guided-mode light 2027 a is provided by the light source 2024, whichmay be or comprise a spotlight, light bulb, LED, or other suitable lightsource. The light 2027 a passes through the light guide 2012 to providetransmitted light 2027 b, which may not be substantially deviated by thelight guide 2012 due to the low distortion. The light source 2024 isshown in the figure to include an active element 2024 a such as one ormore LED dies which convert electricity into visible light, and one ormore reflective members 2024 b which help direct some of the light fromthe element 2024 a generally closer to an optical axis 2021 of the lightsource 2024. The light source 2024 may be mounted such that the opticalaxis 2021 is misaligned a desired amount relative to an optical axis2001 of the light guide 2012 as shown in the figure, or the light source2024 may instead be mounted such that the optical axes 2021, 2001 aresubstantially coincident, or substantially parallel but spaced apartfrom each other.

Relative aspects and features of (1) the light sources 2014 a, 2014 b,the light guide 2012, and the diffractive surface features 2013, and (2)the light source 2024, can be selected so that the light provided fromthese two subsystems combines to provide the desired overallfunctionality, e.g., a desired appearance to the ordinary user and/or adesired illumination at the reference surface 2022. In some cases, itmay be desirable to configure the diffractive surface features 2013 sothat guided-mode light that is out-coupled by the features 2013 isdirected predominantly in the same or similar direction as light emittedby the light source 2024. For example, in the case of FIG. 20, theprojected light from the light source 2024 enters the major surface 2012b and exits the major surface 2012 a; hence, the diffractive surfacefeatures may be configured to couple more guided-mode light out of themajor surface 2012 a (see light 2017 a) than out of the major surface2012 b (see light 2017 b). In this way, for example, the lighting device2012 can be made to deliver light more efficiently to the referencesurface 2022.

Wavelength- or color-related aspects of the two subsystems can also beconsidered. In some cases, it may be advantageous to configure thesubsystems such that the light 2027 b delivered by the light source 2024has substantially the same or similar color (whether substantiallywhite, or non-white) as the light 2017 a delivered by the light sources,light guide, and diffractive surface features. In other cases, it may beadvantageous for the light 2027 b to have a substantially differentcolor than the light 2017 a. Furthermore, it may be desirable for theoverall illumination at the reference surface 2022 to have certaincharacteristics such as, in some cases, having a substantially uniformcolor, and/or having a specified color such as substantially white, ornon-white.

Note that although only one light source 2024 that projectsnon-guided-mode light through the light guide is shown in FIG. 20,alternative embodiments are contemplated in which a plurality of lightsources, e.g., 2, 3, 4, or more, are provided to project such lightthrough the light guide, e.g. in different directions. Note also that insome cases the additional light sources may be of the same or similardesign as the subsystem encompassed by the light sources 2014 a, 2014 b,the light guide 2012, and the diffractive surface features 2013, inwhich case the overall lighting device may be the same as or similar tothat of FIG. 8.

The lighting device 2010 may also incorporate other features disclosedherein, e.g., it may exhibit a band or pattern of bands having a3-dimensional appearance or shape that changes with viewing position,and it may include a patterned light transmissive layer that opticallycontacts some but not other diffractive surface features to defineindicia, and it may incorporate a patterned low index subsurface layerwithin the light guide, and the diffractive surface features may includediffractive features of different pitches in non-overlapping regions ofthe major surface tailored to extract guided-mode light of differentcolors from the light guide in different directions to provide acolorful appearance to an ordinary user.

FIG. 20 a shows a lighting device 2010 a that may be the same as orsimilar to lighting device 2010 of FIG. 20, except that the light source2024 is replaced by an alternative light source 2034 which projectsnon-guided-mode light through the light guide 2012 using reflected lightor indirect illumination. Elements in FIG. 20 a that are the same as orsimilar to elements in FIG. 20 have the same reference number, andrequire no further explanation. The light source 2024 is removed andreplaced by light source 2034. Light source 2034 includes light sources2034 a, which may be LEDs or other suitable light sources, and which aremounted on support members 2035. The sources 2034 a may have the same orsimilar emission characteristics, or instead they may have substantiallydifferent emission characteristics. The support members 2035 mayfunction as heat sinks for the light sources 2034 a, and for lightsources 2014 a, 2014 b. The light source 2034 also includes acustom-formed reflector 2034 b. The reflector 2034 b may be or comprisea molded or thermoformed optical body which may be or include athermoformed multilayer optical film, or other suitable reflectivelayer. If a multilayer optical film is used, the film may be tailored toreflect light broadly over substantially the entire visible spectrum, orit may selectively reflect some visible wavelengths and selectivelytransmit other visible wavelengths, which reflection and transmissionmay change as a function of incidence angle of the light from thesources 2034 a. In any case, the reflector 2034 b substantially reflectslight that is incident from the sources 2034 a as reflected light 2037a, and this light 2037 a then passes as non-guided-mode light throughthe light guide 2012 to provide transmitted light 2037 b. Thetransmitted light 2037 b may not be substantially deviated by the lightguide 2012 due to the low distortion. The light sources 2034 a andreflector 2034 b are shown to be symmetrically disposed relative to theoptical axis 2001 of the light guide 2012, but alternative arrangementsin which the light sources 2034 a and/or reflector 2034 b are notsymmetrically disposed are also contemplated.

Another component or feature discussed near the beginning of thisdetailed description is incorporating into the lighting device otherlight guides having diffractive surface features formed thereon, as wellas a framework of interconnected support members, which may be attachedto multiple such light guides and may contain light sources to injectlight into the light guides. Lighting devices that make use of suchcombinations are shown in FIGS. 21 through 38.

In FIG. 21, a lighting device 2110 includes a group of flat sector- orpie-shaped light guides 2112 and discrete light sources 2114, the lightguides 2112 being suitable for being combined together with light guidesof the same or similar design to provide a lighting device with an evenlarger extended emitting area. Each of the light guides 2112 includesdiffractive surface features (not shown in FIG. 21) formed on at leastone major surface thereof to couple guided-mode light out of the lightguide, as is discussed at length elsewhere herein. The light guides 2112may be affixed to each other in an alternating tiling arrangement asshown so the resulting group of light guides extends along they-direction. In this arrangement, straight side surfaces of adjacentlight guides 2112 are affixed to each other. The various light guides2112 may all have the same nominal design features, e.g. the same pitchconfiguration of diffractive surface features, or light guides ofdiffering design may instead be used. One, some, or all of the lightguides 2112 may be the same as or similar to light guide 1412 of FIG.14.

The device 2110 also includes a plurality of discrete light sources 2114distributed along the curved side surfaces of the light guides 2112 toinject light therein. In alternative embodiments the light sources maybe long and extended rather than discrete. The light sources 2114 mayall be of the nominally same design, e.g., nominally the same outputspectrum (color), output power, and physical dimensions. For example,the light sources 2114 may all emit substantially white light.Alternatively, two or more of multiple light sources may substantiallydiffer in design, e.g., they may have different output spectra (e.g. onemay emit red light, another may emit green light, another may emit bluelight, another may emit white light, and so forth), or different outputpowers. If three distinct packet types of diffractive surface featuresare used for each light guide 2112, e.g. a red, green, and blue packettype as shown in FIG. 14, then the light sources 2114 for each lightguide 2112 may comprise or consist essentially of one or more red lightsource, one or more green light source, and one or more blue lightsource.

In some cases, the light guides 2112 may be affixed to each otherdirectly, such as by a suitable adhesive film or layer. In other cases,they may be connected to each other by a framework of interconnectedsupport members. Such frameworks are discussed in greater detail inconnection with FIGS. 24 and 25 below. The light sources 2114 may beincorporated into the framework. In some cases, one or more supportmembers may be disposed between adjacent light guides, e.g., at thejunctions of flat side surface pairs of the light guides 2112. In suchcases, some or all of the light sources 2114 may be repositioned suchthat they are disposed on or in the support members between adjacentpairs of light guides, similar to the arrangement shown in FIG. 24below.

The light guides 2112 may be substantially coplanar, e.g., orientedparallel to the x-y plane to within manufacturing tolerances, or theymay be non-coplanar. If non-coplanar, they may be arranged into aconcave shape as discussed below in connection with FIGS. 32 and 33, orinto other shapes. Whether planar or non-coplanar, the diffractivesurface features for each light guide 2112 may be configured to coupleguided-mode light preferentially out of one of the opposed majorsurfaces, designated an output major surface of the light guide, and theoutput major surfaces for some or all of the light guides 2112 may facegenerally in a same direction. For example, if the light guides arecoplanar, the output major surfaces may have surface normal vectors thatare all parallel to the z-axis and all pointing in the same direction(either the +z direction or the −z direction), such that the scalarproduct of the surface normal vectors, for some or all possiblecombinations of two light guides within the group of light guides, ispositive. If the light guides are not coplanar, the surface normalvectors for the output major surfaces may be pointing in directions thatare not parallel, but which may all have vector components along aparticular direction (such as the +z direction or the −z direction) suchthat again the scalar product of the surface normal vectors, for some orall possible combinations of two light guides within the group of lightguides, is positive.

FIG. 22 shows a lighting device 2210 that may have the same or similarfeatures as discussed above in connection with lighting device 2110.However, rather than sector- or pie-shaped light guides, the device 2210uses triangle-shaped light guides 2212. Again, each of the light guides2212 includes diffractive surface features (not shown in FIG. 22) formedon at least one major surface thereof to couple guided-mode light out ofthe light guide. The light guides 2212 may be affixed to each other inan alternating tiling arrangement as shown so the resulting group oflight guides extends along the y-direction. In this arrangement, longside surfaces of adjacent light guides 2212 are affixed to each other.The various light guides 2212 may all have the same nominal designfeatures, e.g. the same pitch configuration of diffractive surfacefeatures, or light guides of differing design may instead be used. Thediffractive surface features may be curved or straight in plan view, andmay have any desired orientation relative to the side surfaces of agiven light guide.

The device 2210 also includes a plurality of light sources (not shown),which may be disposed along side surfaces (shown generally at 2212-1)that are exterior to the shape formed by the collection of light guides2212, and/or along side surfaces (shown generally at 2212-2) that areinterior to the overall shape. The light sources may be as describedabove in connection with lighting device 2110.

The light guides 2212 may be affixed to each other directly, or by aframework of interconnected support members as discussed above inconnection with lighting device 2110. Such support members mayincorporate the light sources and may be disposed at the exterior sidesurfaces (shown generally at 2212-1) and/or at interior side surfaces(shown generally at 2212-2).

The light guides 2212 may be substantially coplanar, or non-coplanar,and if the latter, then they may be arranged into a concave shape, orinto other shapes. Whether planar or non-coplanar, the diffractivesurface features for each light guide 2212 may be configured to coupleguided-mode light preferentially out of one of the opposed majorsurfaces, designated an output major surface of the light guide, and theoutput major surfaces for some or all of the light guides 2212 may facegenerally in a same direction as discussed in connection with lightingdevice 2110.

FIG. 23 shows a lighting device 2310 that may have the same or similarfeatures as discussed above in connection with lighting device 2210.Similar to device 2210, device 2310 uses triangle-shaped light guides2312. Again, each of the light guides 2312 includes diffractive surfacefeatures (not shown in FIG. 22) formed on at least one major surfacethereof to couple guided-mode light out of the light guide. The lightguides 2312 may be affixed to each other in a complex tiling arrangementas shown so the resulting group of light guides produces a desiredoverall shape. The various light guides 2312 may all have the samenominal design features, e.g. the same pitch configuration ofdiffractive surface features, or light guides of differing design mayinstead be used. The diffractive surface features may be curved orstraight in plan view, and may have any desired orientation relative tothe side surfaces of a given light guide.

The device 2310 also includes a plurality of light sources (not shown),which may be disposed along side surfaces (shown generally at 2312-1)that are exterior to the shape formed by the collection of light guides2312, and/or along side surfaces (shown generally at 2312-2) that areinterior to the overall shape. The light sources may be as describedabove in connection with lighting device 2210.

The light guides 2312 may be affixed to each other directly, or by aframework of interconnected support members as discussed above inconnection with lighting device 2210. Such support members mayincorporate the light sources and may be disposed at the exterior sidesurfaces (shown generally at 2312-1) and/or at interior side surfaces(shown generally at 2312-2).

The light guides 2312 may be substantially coplanar, or non-coplanar,and if the latter, then they may be arranged into a concave shape, orinto other shapes. Whether planar or non-coplanar, the diffractivesurface features for each light guide 2312 may be configured to coupleguided-mode light preferentially out of one of the opposed majorsurfaces, designated an output major surface of the light guide, and theoutput major surfaces for some or all of the light guides 2312 may facegenerally in a same direction as discussed in connection with lightingdevice 2210.

In FIGS. 24 and 25, details of lighting devices are shown in which aplurality of light guides are attached to a framework of interconnectedsupport members, the support members containing a plurality of lightsources to inject light into the light guides. The light guides includediffractive surface features on one or both major surfaces thereof tocouple guided-mode light out of the light guide, as disclosed herein.The individual light guides shown in these figures are triangular inshape, but the reader will understand that the framework can be readilyreconfigured to accommodate light guides of virtually any shape orconfiguration.

FIG. 24 shows a portion of a lighting device 2410 comprising lightguides 2412, diffractive surface features (not shown) as discussedherein on at least one major surface of the light guides, and lightsources 2414 disposed to inject light into the light guides. Thelighting device 2410 may be substantially similar to the lightingdevices of FIGS. 22 and 23, for example. The light sources 2414 aredisposed in or on support members 2413 a, 2413 b, 2413 c, which areinterconnected with each other to form a framework 2413. The lightguides attach to the framework 2413, and the framework supports thelight guides 2412 and holds them in place in their desired relativepositions.

In the configuration of FIG. 24, the support members are provided alongside surfaces that are interior to the shape formed by the collection oflight guides, e.g. as shown generally at 2212-2 in FIG. 22 and at 2312-2in FIG. 23. This can be contrasted with support members 2513 a, 2513 b,2513 c in FIG. 25, which are provided along side surfaces that areexterior to the shape formed by the light guides. Thus, in FIG. 25, aportion of a lighting device 2510 includes light guides 2512,diffractive surface features (not shown) as discussed herein on at leastone major surface of the light guides, and light sources 2514 disposedto inject light into the light guides. The lighting device 2510 may besubstantially similar to the lighting devices of FIGS. 22 and 23, forexample. The light sources 2514 are disposed in or on support members2513 a, 2513 b, 2513 c, which are interconnected with each other to forma framework 2513. The light guides attach to the framework 2513, and theframework supports the light guides 2512 and holds them in place intheir desired relative positions.

In some cases, a lighting device as disclosed herein may use a frameworkthat has support members disposed only at interior side surfaces of thegroup of light guides, as shown in FIG. 24. In other cases, a lightingdevice as disclosed herein may use a framework that has support membersdisposed only at exterior side surfaces of the light guides, as shown inFIG. 25. In still other cases, a lighting device as disclosed herein mayuse a framework that has one or more support members disposed atinterior side surfaces of the light guides, in combination with one ormore support members disposed at exterior side surfaces of the lightguides. A support member that is disposed at an interior side surfaceconnects to more than one light guide at at least some points along thelength of the support member; for example, support member 2413 aconnects to two light guides 2412 disposed on opposite sides of thesupport member 2413 a. In contrast, a support member that is disposed atan exterior side surface connects to only one of the light guides at anygiven point along the length of the support member; for example, at anygiven point along the support member 2513 b, the support member connectsto only one light guide.

Attachment of a given light guide to a given support member may beaccomplished by any known technique, including through the use of asuitable adhesive layer or material, and/or mechanical connections suchas a press-fit joint or a tongue-in-groove joint.

The support members of FIGS. 24 and 25 may be made of any suitablematerial, and have any suitable construction configuration. For example,the support members may be made of suitable metals, plastics, or othersuitable materials. The support members may be hollow or solid, and mayhave any suitable cross-sectional shape including rectangular, square,circular, elliptical, or of another desired shape, which may be constantor variable along the length of a given support member. Since lightsources are provided in or on at least some of the support members, itis advantageous for the support members to be shaped to accommodate thelight sources, as well as electrical wires or other electricalconnections that can connect the light sources to one or more powersupplies capable of energizing the light sources. To prevent overheatingof the light sources and allow for increased drive currents, it isdesirable for the support members to have a relatively high thermalconductivity so that heat can be drawn away from the light sources toprevent overheating.

Additional lighting devices that incorporate multiple light guides areshown in FIGS. 26-30. In these figures, for simplicity, only the lightguides with their respective plan view sizes, shapes, and relativeconfigurations are shown, but it will be understood that light sourcesand diffractive surface features as disclosed herein, as well as anoptional supporting framework, are also assumed to be present. The lightsources may be provided on interior side surfaces and/or exterior sidesurfaces of the collection of light guides, as exemplified in FIGS. 24and 25. The light guides may be substantially coplanar, or they may benon-coplanar as discussed further below. Whether planar or non-coplanar,the diffractive surface features for each light guide may be configuredto couple guided-mode light preferentially out of one major surface,designated the output major surface, of the light guide, and the outputmajor surfaces for some or all of the light guides may face generally ina same direction, as discussed above.

In FIG. 26, a lighting device 2610 is composed of four light guides 2612having the same or similar square or diamond shape. The light guides2612 are grouped together, and may be attached to each other e.g. usinga suitable framework, to form an overall shape that is also a square ordiamond shape. In FIG. 27, a lighting device 2710 is composed of sevenlight guides 2712 having the same or similar hexagonal shape. The lightguides 2710 are grouped together, and may be attached to each other e.g.using a suitable framework, to form an overall honeycomb-like shape. InFIG. 28, a lighting device 2810 is composed of four light guides 2812 ahaving the same or similar octagonal shape, and one square- ordiamond-shaped central light guide 2812 b. The light guide 2812 b fillsa gap formed by the other light guides. In an alternative embodiment,the light guide 2812 b may be omitted and the gap may be left open andunoccupied. In FIG. 29, a lighting device 2910 is composed of four lightguides 2912 having the same or similar elongated rectangular shape. Thelight guides 2912 are arranged to form a substantial gap in the centralportion of the lighting device 2910. In an alternative embodiment, oneor more light guides may be added to partially or fully fill the centralgap. In FIG. 30, a lighting device 3010 is composed of ten light guides3012 having the same or similar pentagonal shape. The light guides 3012are arranged to form a substantial gap in the central portion of thelighting device 3010. In an alternative embodiment, one or more lightguides may be added to partially or fully fill the central gap.

The lighting devices shown and described in connection with FIGS. 21through 30 may also incorporate other features disclosed herein. Forexample, each of the light guides in any of these lighting devices mayinclude: a band or pattern of bands having a 3-dimensional appearance orshape that changes with viewing position; a patterned light transmissivelayer that optically contacts some but not other diffractive surfacefeatures to define indicia; a patterned low index subsurface layerwithin the light guide; and the diffractive surface features may includediffractive features of different pitches in non-overlapping regions ofthe major surface tailored to extract guided-mode light of differentcolors from the light guide in different directions to provide acolorful appearance to an ordinary user.

Furthermore, as already mentioned above, any of the lighting devicesthat employ multiple light guides may have the light guides arranged tobe substantially coplanar, or they may be arranged to be non-coplanar.Furthermore, some light guides may be substantially coplanar while otherlight guides within the same lighting device may be non-coplanar.Substantially coplanar light guides are depicted schematically in FIG.31, and non-coplanar light guides are depicted schematically in FIGS. 32through 38. In FIGS. 32 and 33, the light guides are arranged tocollectively form an open concave shape. In FIGS. 35-38, the lightguides are arranged to collectively form a 3-dimensional concavestructure that is closed and hollow. Light sources, diffractive surfacefeatures, etc. are not shown in these figures for simplicity, but areassumed to be present in accordance with the teachings herein.

In FIG. 31, a lighting device 3110 includes three light guides 3112 thatare arranged to be substantially coplanar, parallel to an x-y plane.Although three light guides are shown, other numbers of light guides maybe used, including only two light guides as well as four, five, or morelight guides. The light guides may be connected to each other e.g. toform a rigid or stable overall structure, and if so, such connectionsmay be made using a framework of interconnected support members asdiscussed above, such as support members 3113. The diffractive surfacefeatures of the light guides may be configured to couple guided-modelight preferentially out of major surfaces which are designated outputmajor surfaces, and the output major surfaces for some or all of thelight guides may face generally in a same direction, e.g., in the +zdirection or in the −z direction, as desired. In such a configuration,the device can direct light more effectively onto a reference surface ofinterest such as a desk or other surface of interest when the device isused as a luminaire to provide illumination at such surface.

In FIG. 32, a lighting device 3210 includes three light guides 3212 thatare arranged to be non-coplanar. The light guides 3212 collectively forman open concave shape. Although three light guides are shown, othernumbers of light guides may be used, including only two light guides aswell as four, five, or more light guides. (The case of two light guidesis shown in FIG. 33, where lighting device 3310 includes light guides3312 connected to each other via an optional support member 3313 to formanother open concave shape.) The light guides may be connected to eachother e.g. to form a rigid or stable overall structure, and if so, suchconnections may be made using a framework of interconnected supportmembers as discussed above, such as support members 3213. The number oflight guides used, and their respective sizes and shapes, and the colorsof the light sources and the design details of the diffractive surfacefeatures, can be selected and combined with a suitable framework suchthat the lighting device has the appearance of a decorative Tiffanylamp.

The diffractive surface features of the light guides may be configuredto couple guided-mode light preferentially out of major surfaces whichare designated output major surfaces, and the output major surfaces forsome or all of the light guides may face generally in a same directionas discussed above, e.g., the scalar product of the surface normalvectors for some or all possible combinations of two light guides withthe group of light guides may be positive. The output major surfaces maybe oriented to direct light generally inwardly with respect to theconcave shape (e.g. generally in the −z direction in FIGS. 32 and 33),or generally outwardly (e.g. generally in the +z direction in FIGS. 32and 33), as desired.

In an alternative embodiment to that of FIG. 32, the light guides may beconfigured such that they collectively form a tubular structure. Forexample, the two outer light guides 3212 in FIG. 32 can be rotated suchthat their free ends connect with each other, forming a tubular(cylindrical) structure with a triangular cross-sectional shape.Similarly, four light guides can be connected together to collectivelyform a tubular structure having a square or rectangular cross-sectionalshape, five light guides can be connected to provide a pentagonal-shapedtubular structure, six light guides can be connected to provide ahexagonal-shaped tubular structure, and so forth.

Another non-coplanar configuration of multiple light guides in alighting device is shown schematically in FIG. 34. In this figure, alighting device 3410 has a plurality of light guides 3412 arranged toform a 3-dimensional spiral or helix. For generality, the light guides3412 are depicted in the figure as small elongated bodies which mayrepresent the centroids and orientations of the respective light guides.However, the light guides 3412 represented by the elongated bodies mayhave a wide variety of shapes and sizes. For example, the light guides2612 of FIG. 26, and the light guides 2712 of FIG. 27, and the lightguides 2812 a of FIG. 28, and the light guides 2912 of FIG. 29, and thelight guides 3012 of FIG. 30, may all be arranged into helical shapes asshown generally by the light guides 3412 of FIG. 34. In some cases, theindividual light guides that make up the helix may all have the same orsimilar shape and size (e.g., all rectangular, or all pentagonal, or allhexagonal, or all octagonal, etc.), and in other cases the individuallight guides may be of different shapes and/or sizes. The light guidesare preferably connected to each other, e.g. via a framework ofinterconnected support members as discussed in connection with FIGS. 24and 25.

In still other cases, non-coplanar light guides in a lighting device maybe arranged to form a 3-dimensional structure that is closed and hollow.Non-limiting examples of such lighting devices are shown in FIGS. 35-38.Again, for simplicity, these figures do not show light sources,diffractive surface features, and optional frameworks, but they areassumed to be present in accordance with the teachings herein. In viewof the fact that these lighting devices are closed and hollow, it isdesirable in at least some cases to utilize diffractive surface featuresthat are configured to couple guided-mode light preferentially out ofmajor surfaces which are designated output major surfaces, with thesurface normal vectors of the output major surfaces pointing indirections generally away from the interior of the closed structure sothat light is preferentially directed outwardly from the lightingdevice.

In FIG. 35, a light source 3510 is made up of six generallysquare-shaped light guides 3512 connected together, e.g. with aframework of interconnected support members, to form a cube. In FIG. 36,a light source 3610 is made up of twelve generally pentagonal-shapedlight guides 3612 connected together to form a dodecahedron. In FIG. 37,a light source 3710 is made up of twenty generally triangular-shapedlight guides 3712 connected together to form an icosahedron. In FIG. 38,a light source 3810 is made up of a combination of hexagonal-shapedlight guides 3812 a and pentagonal-shaped light guides 3812 b which arearranged and connected together to form a soccer ball-shaped structure.The reader will understand that a wide variety of closed, hollow3-dimensional structures can be made, and are not limited e.g. to shapesknown as Platonic solids.

In the preceding figures, both for lighting devices having only onelight guide and for lighting devices having multiple light guides, thelight guides are generally shown as being flat. This is done forsimplicity, but it need not be a restriction on the disclosed lightingdevices. The lighting devices herein may instead use one or more lightguides that are non-flat. Some examples of non-flat light guides areshown in FIGS. 39 a through 39 c as light guides 3912 a, 3912 b, and3912 c respectively. A non-flat light guide may be curved in the form ofan arc as with light guide 3912 c, or it may have a wavy shape as withlight guides 3912 a, 3912 b. The light guides of FIGS. 39 a-39 c areshown to be curved in the y-z plane but not the x-z plane, butalternative light guides may be curved in the two orthogonal planes,e.g., the y-z plane and the x-z plane. The light guides of FIGS. 39 a-39c are shown as being curved, but alternative non-flat light guides maybe segmented (e.g. piecewise flat but bent in one or more places) ratherthan curved, or both segmented and curved. Whether a given light guideis flat, non-flat, simply curved, complex curved, segmented, and soforth, the light guide generally still has opposed major surfaces, andone or more side surfaces through which light may be injected to provideguided-mode light as discussed herein.

In some cases, a non-flat light guide used in the disclosed lightingdevices may “wrap around itself” (figuratively speaking) to form a tube,such as a cylinder or cone. Examples of such non-flat tubular lightguides are provided in FIGS. 39 d and 39 e. In FIG. 39 d, a light guide3912 d is in the form of a right circular cylinder, having one majorsurface facing outwardly, an opposed major surface facing inwardly, andtwo open ends. At each of the open ends is an annular-shaped sidesurface through which light may be injected to provide guided-modelight. In alternative embodiments the cylinder may have a non-circularcross-sectional shape in the y-z plane, e.g., it may have an ellipticalshape or polygonal shape in cross section. In FIG. 39 e, a light guide3912 e is in the form of a truncated cone, having one major surfacefacing generally outwardly, an opposed major surface facing generallyinwardly, and two open ends. Similar to the cylindrical light guide 3912d, an annular-shaped side surface is disposed at each of the open endsof the light guide 3912 e. One or more light sources may be positionedat one or both annular side surfaces of the light guide to inject lightinto the tubular light guide.

In some cases, the disclosed lighting devices may use multiple lightguides that are not directly connected to each other. One suchembodiment is shown in FIG. 40. There, a lighting device 4010 utilizesmultiple light guides 4012 that are disposed in close proximity to eachother. Each of the light guides is provided at least with one or morelight sources to inject light into the light guide, and diffractivesurface features to couple the resulting guided-mode light out of thelight guide. The directionality, brightness (luminous output), and colorof the various light guides 4012 may be tailored as desired to provide adesired illumination at a reference surface of interest, as well as adesired appearance to the ordinary user. Some or all of the light guides4012 may have the same size, shape, and configuration, and some or allof the light guides 4012 may have substantially different sizes, shapes,and/or configurations. The light guides 4012 may all be suspended fromor otherwise connected to a single support hub, such as a plate adaptedto be affixed to a ceiling.

Numerous modifications can be made to the disclosed embodiments withinthe scope of the present description. For example, since the lightguides can be made with low optical distortion, the disclosed devicescan serve the dual function of a lighting device (such as a luminaire)and a window. When the light source(s) injecting light into the lightguide are powered “on” or energized, the device may function primarilyor exclusively as a lighting device. When the light source(s) arepowered “off” or de-energized, the device may function primarily orexclusively as a window. If suitably mounted in a ceiling or roof of ahome, building, factory, or similar structure, the device may functionas a skylight to allow natural sunlight to enter the structure. Thedevice may similarly be mounted (e.g. horizontally or at an incline) ina ceiling or roof of an automobile, truck, boat, airplane, or othermobile land-, water-, or air-vehicle for use as a sunroof or moonroof,the device also having the functionality of being able to provideillumination (e.g. at night) by energizing the light source(s). Inaddition to being mounted in ceilings or roofs, the disclosed devicescan be suitably mounted (e.g. vertically) in walls or panels ofstationary structures such as homes, buildings, etc., or of mobilevehicles such as automobiles, boats, etc., for use as a window throughwhich objects can be perceived and/or through which natural sunlight canpass. Thus, for example, the object 124 in FIG. 1, the object 824 inFIG. 8, the light source 2024 in FIG. 20, and the light source 2034 inFIG. 20 a, may be (or may be supplemented with) the sun, the moon, orother sources of natural light.

Furthermore, any and all of the disclosed lighting devices, includingboth those that have only one light guide and those that have multiplelight guides, can be tailored to provide illumination of a desired colorand a desired color uniformity at a reference surface of interestproperly disposed relative to the lighting device, by appropriateselection of light sources and diffractive surface features, asdiscussed elsewhere herein. Thus, if desired, the light guide(s) andtheir respective light sources and diffractive surface features can beselected to provide illumination of a substantially uniform color, whichmay be a substantially white color or a non-white color, at thereference surface.

Furthermore, any and all of the disclosed lighting devices (includingthose defined in each of the claims below) can include or exhibit, or bereadily modified or adapted to include or exhibit, one, some, or all ofthe various features disclosed herein, including but not limited to: aband or pattern of bands having a 3-dimensional appearance or shape thatchanges with viewing geometry; a patterned light transmissive layer thatoptically contacts some but not other diffractive surface features todefine indicia; a subsurface a patterned low index subsurface layerwithin the light guide; diffractive features of different pitches innon-overlapping regions of the major surface; the light guide(s) mayhave a low optical distortion such that they can be used as windows inan “off” state; the light guide(s) may have a colorful appearance whenviewed directly, but may provide illumination of a substantially uniformcolor on a reference surface of interest.

EXAMPLE 1

A lighting device suitable for use as a luminaire was made andevaluated. The device was similar in design to that of FIGS. 12, 12 a,and 13. The device incorporated a circular-shaped light guide withdiffractive surface features in the form of a spiral pattern, thediffractive surface features arranged into repeating patterns of sixpacket types with different groove or prism pitches. A mounting ring wasused to position thirty-six equally spaced LEDs around the curved sidesurface of the light guide to inject light into the light guide. Furtherdetails of construction will now be given.

A precision diamond turning machine was used to cut a spiral-shapedgroove pattern, which became the diffractive surface features in thelighting device after replication, into the copper surface of acylindrical tool. The diamond was shaped so that the grooves had asawtooth (asymmetric) profile in cross section similar to FIG. 6, with aheight-to-pitch ratio (see FIG. 6) of about 1:1. During cutting, thegroove pitch of the spiral was cycled between six specific values (315nm, 345 nm, 375 nm, 410 nm, 445 nm, and 485 nm) to produce groovepackets which formed nested annular regions that bordered each other butdid not overlap with each other. Each annular region was a groove packetof constant pitch, and each set of six adjacent annular regions formed arepeating group or set of groove packets. The spiral pattern had anoverall diameter of about 8 inches (about 20 centimeters). The radialdimensions or widths of the annular regions were selected so that theaggregate area for all of the six pitch values was the same. That is,the area of the entire grooved pattern was about 314 cm² (πr², wherer≈10 cm), and the aggregate area for grooves having the 315 nm pitch wasabout 314/6≈52 cm², and the aggregate areas for grooves having each ofthe other five pitches was also about 52 cm². The annular regions wererelatively narrow as measured radially, the maximum such dimension beingabout 150 micrometers.

The grooved surface of the resulting copper tool was then replicated ina thin flexible light-transmissive film (see e.g. layers 1111 b and 1111c in FIG. 11) using a cast-and-cure technique. This was done by coatingthe grooved surface of the copper tool with an organic phosphonic acidrelease layer (commonly known to those skilled in the art), and castingan acrylate resin composition against the coated precision tool using atransparent polyethylene terephthalate (PET) support film having athickness of about 5 mils (about 125 micrometers). The acrylate resincomposition included acrylate monomers (75% by weight PHOTOMER 6210available from Cognis and 25% by weight 1,6-hexanedioldiacrylateavailable from Aldrich Chemical Co.) and a photoinitiator (1% by weightDarocur 1173, Ciba Specialty Chemicals). The resin composition was thencured using ultraviolet light. This resulted in a microreplicatedoptical film about 125 microns thick and having diffractive surfacefeatures in the form of a negative or inverted version (negativereplica) of the spiral-shaped groove pattern from the precision coppertool. The refractive index of the PET support film was about 1.49 andthe refractive index of the cured acrylate resin was about 1.5. Themicroreplicated optical film had a transparent appearance when viewed atan angle normal to the surface of the film, with a slightly blue hue.Objects could be viewed through the film with low distortion.

Excess material around the spiral pattern was cut away so that themicroreplicated film was circular in shape. The film was directlyattached to one major surface of a clear, light-transmissive circularacrylic plate of thickness 3 mm, the plate also having a diameter ofabout 20 cm. Attachment was accomplished using a 1 mil (approximately 25micrometer) thick optically clear pressure sensitive adhesive (Vikuiti™OCA 8171 from 3M Company), with the microreplicated surface of the filmfacing away from the plate and exposed to air, and with substantially noair gaps between the film and the plate. The combination of the plateand the film resulted in a light guide with diffractive surface featureson (only) one major surface thereof for light extraction, the lightguide having a diameter of about 20 cm and a thickness of about 3 mm.

A string of 36 nominally identical LEDs (product code NCSL119T-H1 fromNichia), each LED emitting white light (“warm white”) in a divergentdistribution, was used for light injection into the light guide. TheLEDs were mounted in a ring-shaped bezel so that they were equallyspaced in 10 degree increments around the circular side surface of thelight guide, each LED pointed towards the center of the light guide anddisposed immediately adjacent the side surface to directly inject lightinto the light guide. For improved efficiency, strips of highreflectivity mirror film (3M™ Vikuiti™ ESR) were laminated on the insidesurface of the mounting ring between every two neighboring LEDs, themirror film strips also being immediately adjacent to the circular sidesurface of the light guide.

The lighting device so constructed was connected to a power supply andsuspended from the ceiling of a room. FIG. 41 a is a photograph of thelighting device with the power supply turned off and ambient room lightsturned on. The viewing direction for this photograph was slightlyoblique, i.e., not directly beneath the lighting device along itssymmetry or optical axis, but at a moderate angle relative to such axis.Note that details of the ceiling can be seen through the light guidewith little or no significant distortion. Wires used to suspend thelighting device and connect it to the power supply can also be seenthrough the light guide. In this “off” state, the light guide had aslightly bluish hue similar to that of the microreplicated film byitself.

FIG. 41 b is a photograph of the same lighting device at a somewhat moreoblique viewing angle relative to that of FIG. 41 a, but also with thepower supply (and thus all 36 LEDs) turned on and the ambient roomlights turned off Variable color hues could be seen at different areasof the light guide, the colors not being visible in the grayscalephotograph of FIG. 41 b. Bright bands could also be seen over the outputarea of the light guide, one band for each of the 36 energized lightsources, and these bands are plainly visible in FIG. 41 b. The bands canbe seen to form a pattern having a 3-dimensional appearance. Whenobserved at other viewing directions, the bright bands changed shape,and variable color hues could be seen across the light guide atvirtually any viewing direction. Three small areas or points 4110 b,4112 b, 4114 b are identified in the photograph on the output area ofthe light guide between adjacent bright bands. The color at each ofthese points was measured in terms of the known CIE chromaticity (x,y)coordinates. The CIE (x,y) color coordinates, which are dimensionless,should not be confused with spatial (x,y) coordinates e.g. as in theCartesian x-y-z coordinate systems shown in various figures herein. Themeasurement of color was done using a camera configured as acolorimeter, type PR-650 SpectraScan™ from Photo Research Inc.,Chatsworth, Calif. Visually, the area 4110 b had a dark red color, andis plotted as point 4110 c on the CIE color coordinate scale of FIG. 41c. The area 4112 b had an orange or brown color, and is plotted as point4112 c on the scale of FIG. 41 c. The area 4114 b had a blue color, andis plotted as point 4114 c on scale of FIG. 41 c. The CIE colordifference between the points 4112 c and 4114 c was 0.25.

The lighting device of Example 1, with its extended area light guide anddiffractive surface features, has the effect of converting the LED lightsources, which when viewed directly with the eye appear as very brightpoint sources, into an extended area source with significantly lowerluminance so that the lighting device can be directly viewed withouthurting the eyes. The diffractive surface features not only serve thefunctional purpose of extracting guided-mode light out of the lightguide, but also enhance the aesthetic appeal of the lighting device byadding attractive colors and the 3-dimensional band pattern when thelighting device is directly observed (e.g. as in FIG. 41 b). We havefound, however, that the aesthetic colors and bands seen by a user whenlooking directly at the lighting device need not detract from theability of the lighting device to provide substantially uniform whitelight illumination for objects and surfaces remote from the lightingdevice.

The remote illumination produced by the Example 1 lighting device on areference surface was tested using the setup shown in FIG. 42 a. In thissetup, item 4210 represents the Example 1 lighting device, suspendedfrom the ceiling. The lighting device 4210 had an optical axis orsymmetry axis 4201 which passed through the center of the disk-shapedlight guide and was perpendicular to the light guide. In the figure, theoptical axis 4201 is parallel to the z-axis of the Cartesian coordinatesystem. A flat reference surface 4212 extended parallel to the x-yplane, and was disposed at a distance D of 2.3 meters from the lightingdevice 4210, as measured along the optical axis 4201. The 2.3 meterdistance D compares to the 20 cm characteristic transverse dimension Lof the light guide (in this case, the maximum, minimum, and averagetransverse dimensions were equal to each other because of the circularshape of the light guide) by a factor of 10.1. The flat surface 4212 wascovered with a white diffusely reflective film (product code DLR80 fromE.I. du Pont de Nemours and Company) having a 98% reflectivity forvisible light. A camera 4216 was then positioned as shown, oriented atan angle of about 30 degrees relative to the optical axis 4201, toobtain a color image of the white diffuse surface as illuminated solelyby the Example 1 lighting device 4210. The PR-650 camera mentioned abovewas used as the camera 4216.

Due to the circular symmetry of the Example 1 lighting device, theillumination provided on the reference surface 4212 was alsosubstantially circularly symmetric. This allowed us to effectivelyevaluate the color of the illumination over the entire (circular)measurement portion of the reference surface by measuring the color of asingle row of small areas or points, which are collectively labeled 4214in the figure. (Although 8 areas or points 4214 are shown in the figure,a total of 7 points were used for the measurements reported here.) Thecolor at each of these small areas was measured using the PR-650 camera.The small areas were equally spaced along the x-axis, from a first area4214 a, which was aligned with the optical axis 4201, to a last area4214 i. Maximum illuminance Imax occurred at approximately the centrallylocated first area 4214 a, and the illuminance dropped to Imax/e at adistance (radius) of about 1.85 meters from the central point or area4214 a. The distance from the first area 4214 a to the last area 4214 iwas 183 cm, i.e., about 1.85 meters. The color measurements thus fairlyrepresented the color variations present in a 3.7 meter diametermeasurement portion corresponding to an illuminance threshold of Imax/e.Visually, the illuminated flat surface 4212 appeared nominally whitewith good spatial color uniformity over the measurement portion.

The measured CIE color coordinates for the areas 4214 are plotted on theCIE color coordinate scale of FIG. 42 b. The measured colors define acurve 4223, having one endpoint corresponding to the color at area 4214a, and an opposite endpoint corresponding to the color at area 4214 i.The camera 4216 thus measured a non-zero color variability within theImax/e measurement portion for the lighting device 4210. However, thecolor variability was relatively small: the CIE color difference betweenthe endpoints of the curve 4223 is 0.053. The overall color variabilitythroughout the Imax/e measurement portion was thus less than 0.08, 0.07,and 0.06. Furthermore, all of the measured points on the curve 4223remain close to the Planckian locus, and are within a substantiallywhite region of the color spectrum.

Additional measurements were then taken for this Example 1 insubstantially the same way as described above, except that the referencesurface 4212 was positioned at a distance D of 1 meter, rather than 2.3meters, from the lighting device 4210. This reduced the diameter of theImax/e measurement portion from 3.7 meters to 1.83 meters. Colormeasurements were again taken by the camera 4216 along the single row ofsmall equally spaced areas or points 4214, a first such area beingaligned with the optical axis 4201, and having a maximum illuminanceImax, and a last such area being disposed at a distance of 91.4 cm fromthe first area, and having an illuminance of about Imax/e. The colormeasurements thus fairly represented the color variations present in a1.83 meter diameter measurement portion corresponding to an illuminancethreshold of Imax/e. Visually, the illuminated flat surface 4212appeared nominally white, with a spatial color uniformity within theImax/e measurement portion that was about as good as was measured at adistance D of 2.3 meters.

The measured CIE color coordinates for the areas 4214, for the case ofD=1 meter, are also plotted on the CIE color coordinate scale of FIG. 42b. The measured colors define a curve 4222, having one endpointcorresponding to the color at the first area 4214 a, and an oppositeendpoint corresponding to the color at the last area 4214 i. The camera4216 thus measured a non-zero color variability within the Imax/emeasurement portion for the lighting device 4210 for a reference surfacedisposed at this distance D=1 meter. However, the color variability wasagain relatively small: the CIE color difference between the endpointsof the curve 4222 is 0.059. The overall color variability throughout theImax/e measurement portion was thus less than 0.08, 0.07, and 0.06.Furthermore, all of the measured points on the curve 4223 remain closeto the Planckian locus, and are within a substantially white region ofthe color spectrum.

Still more measurements were then taken for this Example 1 insubstantially the same way as described above, except that the referencesurface 4212 was positioned at a distance D of 0.5 meters, rather than 1or 2.3 meters, from the lighting device 4210. This reduced the diameterof the Imax/e measurement portion to 0.91 meters. Color measurementswere again taken by the camera 4216 along the single row of smallequally spaced areas or points 4214, a first such area being alignedwith the optical axis 4201, and having a maximum illuminance Imax, and alast such area being disposed at a distance of 45.7 cm from the firstarea, and having an illuminance of about Imax/e. The color measurementsthus fairly represented the color variations present in a 0.91 meterdiameter measurement portion corresponding to an illuminance thresholdof Imax/e. Visually, the illuminated flat surface 4212 appearednominally white, with a spatial color uniformity within the Imax/emeasurement portion that was not as small as was measured at distances Dof 2.3 meters and 1 meter.

The measured CIE color coordinates for the areas 4214, for the case ofD=0.5 meters, are also plotted on the CIE color coordinate scale of FIG.42 b. The measured colors define a curve 4221, having one endpointcorresponding to the color at the first area 4214 a, and an oppositeendpoint corresponding to the color at the last area 4214 i. The camera4216 thus measured a non-zero color variability within the Imax/emeasurement portion for the lighting device 4210 for a reference surfacedisposed at this distance D=0.5 meter. The color variability wascharacterized by a CIE color difference between the endpoints of thecurve 4221 equal to about 0.078. The overall color variabilitythroughout the Imax/e measurement portion was thus less than 0.08.Furthermore, all of the measured points on the curve 4223 remain closeto the Planckian locus, and are within a substantially white region ofthe color spectrum.

EXAMPLE 2

Another light source was combined with the lighting device of Example 1to provide a modified lighting device. The additional light source was aconventional flashlight that could be positioned behind the light guideand pointed so as to project light from the flashlight through the lightguide as non-guided-mode light, onto reference surfaces of interest. Thedistortion of the light guide was low, such that light from theflashlight was not substantially deviated by the light guide. Themodified lighting device could be controlled such that the LED lightsources injecting light into the light guide could be powered “on” whilethe flashlight was powered “off”, or vice versa, or both the LED lightsources and the flashlight could be powered “on” to provide a combinedillumination onto reference surfaces of interest.

EXAMPLE 3

Another lighting device suitable for use as a luminaire was made andevaluated. The device incorporated a rectangular-shaped light guide withdiffractive surface features. The diffractive surface features were aportion of the spiral-shaped groove pattern described in Example 1, theportion taken from a central rectangular region of the spiral pattern. Alight source module was mounted along one of the short edges of therectangular light guide, the light source module containing one row ofeighteen equally spaced individual, discrete light sources, the lightsources being nominally identical LEDs each emitting white light in adivergent distribution. The light guide also incorporated a patternedlow index subsurface layer in the form of a random gradient dot pattern.Further details of construction will now be given.

The following ingredients were combined in a 1-liter wide-mouth amberbottle: 5.70 g of an aliphatic urethane oligomer (product code CN 9893from Sartomer Company, Exton, Pa.), and 22.40 g of pentaerythritoltriacrylate (product code SR 444, also from Sartomer Company). Thebottle was capped and shaken for 2 hours to dissolve the CN9893 toproduce a clear batch. This solution, referred to as a resin premix, wascombined with 482.84 g of silane treated (product code Silquest™ A-174from Momentive Performance Materials, Friendly, W. Va.) colloidal silica(product code NALCO 2327 from Nalco Chemical Co., Naperville, Ill.) in a2000 mL poly bottle. These components were mixed by transferring thebatch back and forth between the two bottles, ending with the batch inthe 2000 mL poly bottle. To this bottle was added, 5.84 g of a firstphotoinitiator (product code IRGACURE™ 184 from Ciba Specialty ChemicalsCorp., Tarrytown, N.Y.) and 1.12 g of a second photoinitiator (productcode IRGACURE™ 819, also from Ciba Specialty Chemicals Corp.). Thesolution was shaken for 30 minutes to dissolve the photoinitiators. Theresulting batch was a translucent, low-viscosity dispersion. The batchwas then diluted to about 17.7% solids by weight with a 50/50 blendethyl acetate and propylene glycol methyl ether (available from DowChemical as DOWANOL PM), to yield a coating formulation.

The coating formulation was coated onto a 50 micron thick PET film(MELINEX 617, available from DuPont) using a slot die at a line speed of3.1 meters/minute. The wet coating thickness was approximately 8.1microns. In an inert chamber (<50 ppm O₂), the wet coating was partiallycured in-line at the same line speed with UV radiation at 395 nm anddose of 850 mJ/cm². The UV radiation was provided by UV-LEDs availablefrom Cree, Inc. The partially cured coating sample was then dried at 70°C. in a 9 meter oven, and under a nitrogen-purged atmosphere, finallycured with a 236 Watt/cm² Fusion H bulb (available from Fusion UVSystems, Inc.). The resulting nanovoided polymeric layer had a thicknessof 1.3 microns. The transmission was 96.4%, the haze was 1.33%, and theclarity was 99.7%, as measured using a BYK gardner Haze Gard Plus(Columbia, Md.) instrument. The refractive index of the nanovoided layerwas between 1.20 and 1.22 as measured at 589 nm using a Metricon PrismCoupler (Metricon Corporation, Pennington, N.J.).

The nanovoided polymeric layer, still disposed on the 50 micron PETcarrier film, was printed with a UV curable clear ink (UV OP1005 GPVarnish from Nazdar, Shawnee, Kans.) using an indirect gravure printingprocess. A flexographic tool was fabricated to have a random 100 microngradient dot pattern, the density of the dots varying in an in-planex-direction and being relatively constant in an orthogonal in-planey-direction. The gradient pattern was similar to that shown in thephotograph of FIG. 43. A gravure roll (pyramidal and 9 cubic microns persquare micron) was rated to give a wet coating of approximately 9.65microns. The printing was done at 10 meters per minute with highintensity UV curing under a nitrogen-purged atmosphere with a 236Watt/cm² Fusion H bulb (available from Fusion UV Systems, Inc.) afterthe printing. The resulting printed layer was made up of: first regionshaving the nanovoided polymeric material, the first regions having afirst refractive index; and second regions having the same nanovoidedpolymeric material but wherein the nanovoids were filled or partiallyfiled with the cured clear ink, the second regions having a secondrefractive index greater than that of the first regions. The opticalfilm consisting of this dot-printed nanovoided layer atop the 50 micronPET carrier film was substantially transparent, and objects could beseen with little distortion when looking through the film. Opticalproperties of this optical film, before being incorporated into thelight guide, were measured using the BYK Gardner Haze Gard Plusinstrument. Measurements made on one side or end of the film, at whichthe random gradient dot pattern had a low density, were: 96.6%transmission; 3.56% haze; and 95.6% clarity. Measurements made on theopposite side or end of the film, at which the random gradient dotpattern had a high density, were: 95.8% transmission; 6.82% haze; and89.9% clarity. Note that the transmission measurements reported here arenot corrected for Fresnel reflections at the outer surfaces of the film.The refractive index of the cured ink was measured to be approximately1.525 as measured on a flat cured sample using a Metricon prism coupler(wavelength of light used to measure the refractive index was 589 nm).

A lighting device was then made using this dot-printed optical filmtogether with a rectangular acrylic plate, a rectangular piece orportion of the microreplicated optical film (having the spiralmulti-pitch diffractive surface features) described above in Example 1,and a linear array of discrete light sources. The dot-printed nanovoidedlayer of the dot-printed optical film was used as a patterned low indexsubsurface layer to spatially control the interaction of guided-modelight with curved diffractive surface features. A rectangular section orpiece was cut out of a microreplicated optical film as described inExample 1, the center of the rectangular piece substantially coincidingwith the center of the spiral groove pattern. The rectangular piece hada major in-plane dimension (length) of about 6 inches (about 150 mm) anda minor in-plane dimension (width) of about 4 inches (about 100 mm). Arectangular acrylic (PMMA) plate was obtained having a major in-planedimension (length) of about 6 inches (about 150 mm), a minor in-planedimension (width) of about 4 inches (about 100 mm), and a thickness of 3mm. A piece of the dot-printed optical film described above was attachedto one of the major surfaces of the acrylic plate using a pressuresensitive adhesive, 3M Optically clear adhesive 8171. The rectangularpiece of the microreplicated optical film was attached to the oppositeside of the dot-printed optical film using an additional layer of 3MOptically Clear Adhesive 8171, such that the microreplicated surface(diffractive surface features) faced away from the acrylic plate and wasexposed to air, and such that the dot-printed nanovoided layer wasburied or sandwiched between the microreplicated film and the acrylicplate with substantially no air gaps between the film pieces and theplate, the dot-printed nanovoided layer thus forming a patterned lowindex subsurface layer. The combination of the films and the plateresulted in a light guide with diffractive surface features on (only)one major surface thereof, the light guide having in-plane dimensions ofabout 6 inches and 4 inches (about 150 mm and 100 mm) and a thickness ofabout 3 mm.

The light guide so constructed was then placed into an illumination testfixture which contained a light source module having eighteen equallyspaced discrete light sources, the light sources being nominallyidentical LEDs (product code NCSL119T-H1 from Nichia), each LED emittingwhite light (“warm white”) in a divergent distribution. The light sourcemodule was mounted along the short side of the light guide. The lightsources were energized with a power supply and photographs were taken ofthe lighting device from various viewing geometries. A strip of blackelectrical tape was placed on one side of the LED array to block straylight, emitted in sideways directions from the LEDs, from reaching thecamera. A photograph of the lighting device when viewed from a positionsubstantially perpendicular to the face of the light guide is shown inFIG. 44 a. In this view, the light sources are on the right side of thisfigure. A photograph of the same lighting device when viewed at anoblique angle to the plane of the light guide is shown in FIG. 44 b. Asa result of the gradient patterned low index subsurface layer, thelighting device exhibited a uniform-appearing luminance distributionwhen looking at the light guide, and also provided, on a diffusivesurface located 1 meter from the light guide approximately along theoptical axis, illumination that was substantially uniform in color.Bright bands associated with the discrete light sources can be clearlyseen in each of the viewing geometries, and the bands were observed tochange in shape and curvature with viewing geometry. Variable color huescould also be seen at different areas of the light guide, but the colorsare not visible in the grayscale photograph of the figures.

EXAMPLE 4

Another lighting device suitable for use as a luminaire was made andevaluated. The device incorporated a circular-shaped light guide withdiffractive surface features. The diffractive surface features filled 36triangle-shaped areas which were uniformly sized and tiled tosubstantially fill the circular area of the light guide. The diffractivesurface features in each of the triangle-shaped areas were straight andparallel to each other, and of a single pitch, although three differenttriangle types of three different pitches were used. A mounting ring wasused to position thirty-six equally spaced LEDs around the curved sidesurface of the light guide to inject light into the light guide. Indiciain the shape of a United States map was formed by patterned printing onthe diffractive surface features. Further details of construction willnow be given.

A precision diamond turning machine was used to cut linear grooves intothe copper surface of a cylindrical tool. The diamond was shaped so thatthe grooves had a sawtooth (asymmetric) profile in cross section similarto FIG. 6, with a height-to-pitch ratio (see FIG. 6) of about 1:1.During cutting, the groove pitch was maintained at a constant value ofabout 310 nm to produce a first single-pitch one-dimensional diffractiongrating tool. This procedure was then repeated in another copper surfaceusing a different groove pitch, the pitch now being maintained at aconstant value of about 345 nm to produce a second single-pitchone-dimensional diffractive grating tool. The procedure was repeated athird time in still another copper surface using a third groove pitch,the third pitch being maintained at a constant value of about 410 nm toproduce a third single-pitch one-dimensional diffractive grating tool.

The grooved surfaces of the resulting three copper tools were thenreplicated in three corresponding thin flexible light-transmissive films(see e.g. layers 1111 b and 1111 c in FIG. 11) using a cast-and-curetechnique. This was done by coating the grooved surface of each coppertool with an organic phosphonic acid release layer (commonly known tothose skilled in the art), and casting an acrylate resin compositionagainst the coated precision tool using a transparent polyethyleneterephthalate (PET) support film having a thickness of about 5 mils(about 125 micrometers). The acrylate resin composition includedacrylate monomers (75% by weight PHOTOMER 6210 available from Cognis and25% by weight 1,6-hexanedioldiacrylate available from Aldrich ChemicalCo.) and a photoinitiator (1% by weight Darocur 1173, Ciba SpecialtyChemicals). The resin composition was then cured using ultravioletlight. This resulted in three microreplicated optical films, each about125 microns thick and having diffractive surface features in the form ofnegative or inverted versions (negative replicas) of the linear groovepattern from the first, second, and third precision copper tools,respectively. The refractive index of the PET support film was about1.49 and the refractive index of the cured acrylate resin was about 1.5.Each of the microreplicated optical films had a transparent appearancewhen viewed at an angle normal to the surface of the film, with aslightly blue hue. Objects could be viewed through each film with lowdistortion.

The microreplicated optical films were then physically cut intotriangle-shaped pieces, twelve such pieces obtained from each of thefirst, second, and third optical films. The pieces were substantiallyidentically shaped into isosceles triangles with two long edges and oneshort edge, the long edges each being about 100 mm in length and theshort edge being about 17 mm in length. The pieces were all cut fromtheir respective optical films such that the diffractive surfacefeatures completely filled one major surface of the triangle piece, andthe individual grooves or prisms of the diffractive surface featureswere all parallel to the short edge of the triangle shape.

All thirty-six of the triangle-shaped pieces of optical film were thendirectly attached to one major surface of a clear, light-transmissivecircular acrylic plate of thickness 3 mm, the plate having a diameter ofabout 20 cm. For the attachment, the triangle-shaped pieces were laidnext to each other in a tiled arrangement with the long edges ofadjacent pieces abutting each other, and with the short edges of thepieces forming a thirty-six sided shape approximating a circle andsubstantially coinciding with the circular outer side surface of theacrylic plate. The film pieces were also arranged in a repeatingsequential 1,2,3,1,2,3, . . . fashion such that any given piece from thefirst film abutted a piece from the second film along one long edge andabutted a piece from the third film along the other long edge.Attachment of the pieces to the plate was accomplished using a 1 mil(approximately 25 micrometer) thick optically clear pressure sensitiveadhesive (Vikuiti™ OCA 8171 from 3M Company), with the microreplicatedsurface of each film piece facing away from the plate and exposed toair, and with substantially no air gaps between each film piece and theplate. The combination of the plate and the thirty-six film piecesresulted in a light guide with diffractive surface features on (only)one major surface thereof for light extraction, the light guide having adiameter of about 20 cm and a thickness of about 3 mm.

A sheet of lined optically clear pressure sensitive adhesive (PSA) wasthen obtained and printed with a curable ink in the pattern of a UnitedStates map. After the ink was cured, the resulting printed sheet wasjoined to the light guide by pressing the printed sheet against thesurface of the microreplicated optical film pieces containing thediffractive surface features. Portions of the PSA layer that were notcoated with the cured ink, corresponding to the background areas of themap image, flowed into and filled the spaces between the diffractivesurface features, so that optical contact was made between the PSAlayer, which had a refractive index of about 1.475, and the diffractivesurface features, which had a refractive index of about 1.5. Portions ofthe PSA layer that were coated with the cured ink, corresponding to theforeground areas of the map image, did not flow into or make opticalcontact with the diffractive surface features due to the presence of theglass-like cured ink. In those areas, a very thin air pocket or layerremained between the cured ink and the diffractive surface features suchthat the diffractive surface features were in optical contact with air.The combination of the light guide (the plate and the optical filmpieces) and the printed sheet resulted in a light guide with diffractivesurface features on (only) one major surface thereof for lightextraction, and with patterned printing forming indicia (a United Statesmap image), the light guide having a diameter of about 20 cm and athickness of about 3 mm.

A string of 36 nominally identical LEDs (product code NCSL119T-H1 fromNichia), each LED emitting white light (“warm white”) in a divergentdistribution, was used for light injection into the light guide. TheLEDs were mounted in a ring-shaped bezel so that they were equallyspaced in 10 degree increments around the circular side surface of thelight guide, each LED pointed towards the center of the light guide anddisposed immediately adjacent the side surface to directly inject lightinto the light guide. For improved efficiency, strips of highreflectivity mirror film (3M™ Vikuiti™ ESR) were laminated on the insidesurface of the mounting ring between every two neighboring LEDs, themirror film strips also being immediately adjacent to the circular sidesurface of the light guide.

The lighting device so constructed was connected to a power supply andplaced sideways on a table in a laboratory setting. With the powersupply turned off and in ambient room light, objects across the roomcould be seen through the light guide with little or no significantdistortion. Furthermore, in this “off” state, the light guide had aslightly bluish hue similar to that of the microreplicated film byitself, and the printed image of the U.S. map could not be easilyperceived. FIG. 45 is a photograph of the lighting device of thisExample 2 with the power supply (and thus all 36 LEDs) turned on and theambient room lights turned off. The U.S. map of the patterned printingis clearly visible, and the contrast between printed regions andremaining regions is high. Variable color hues could also be seen atdifferent areas of the light guide, with different triangle-shaped areashaving different colors (particularly in the foreground areas of the mapimage) which are discernible in FIG. 45 even though the colorsthemselves are not visible due to the grayscale format of thephotograph. Straight radial border features, which are relatively brightand caused by light scattering at the edges of the individualtriangle-shaped pieces, can also be seen in the photograph. In additionto these bright border features, additional fainter radial bands canalso be seen in some places over the output area of the light guide,superimposed on the printed pattern, these fainter bands beingassociated with particular ones of the energized light sources. Thefainter bands are all relatively straight (radial) with little or nocurvature from the viewing geometry of FIG. 45, but their shape changedas a function of viewing angle in a 3-dimensional fashion in the sameway as the bright bands of Example 1 changed. Variable color hues couldalso be seen across the light guide at virtually any viewing direction.

The teachings of this application can be used in combination with theteachings of any or all of the following commonly assigned patentapplication publications, which are incorporated herein by reference andwere filed on the same date as the present application: US 2014/0043846(Yang et al.); US 2014/0043850 (Thompson et al.) (granted as U.S. Pat.No. 8,834,004 (Thompson et al.); and US 2014/0043847 (Yang et al.).

Unless otherwise indicated, all numbers expressing quantities,measurement of properties, and so forth used in the specification andclaims are to be understood as being modified by the term “about”.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and claims are approximations that canvary depending on the desired properties sought to be obtained by thoseskilled in the art utilizing the teachings of the present application.Not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the invention are approximations, to the extent any numerical valuesare set forth in specific examples described herein, they are reportedas precisely as reasonably possible. Any numerical value, however, maywell contain errors associated with testing or measurement limitations.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the spirit and scopeof this invention, and it should be understood that this invention isnot limited to the illustrative embodiments set forth herein. The readershould assume that features of one disclosed embodiment can also beapplied to all other disclosed embodiments unless otherwise indicated.It should also be understood that all U.S. patents, patent applicationpublications, and other patent and non-patent documents referred toherein are incorporated by reference, to the extent they do notcontradict the foregoing disclosure.

The invention claimed is:
 1. A luminaire, comprising: a light guidehaving opposed major surfaces, at least one of the major surfaces havingdiffractive surface features therein adapted to couple guided-mode lightout of the light guide; a first light source configured to inject lightinto the light guide; and a second light source configured to projectlight through the light guide as non-guided-mode light.
 2. The luminaireof claim 1, wherein the light guide has a low optical distortion suchthat the light projected by the second light source is not substantiallydeviated by the light guide.
 3. The luminaire of claim 1, wherein theopposed major surfaces include a first major surface opposed to a secondmajor surface, wherein the projected light from the second light sourceenters the first major surface and exits the second major surface, andwherein the diffractive surface features are configured to couple moreguided-mode light out of the second major surface than out of the firstmajor surface.
 4. A luminaire, comprising: a framework comprising aplurality of interconnected support members; a plurality of light guidesattached to the framework, each of the light guides having opposed majorsurfaces, at least one of the major surfaces of each light guide havingdiffractive surface features therein adapted to couple guided-mode lightout of the light guide; and a plurality of light sources disposed onand/or in the support members, the light sources being distributed toinject light into all of the light guides; wherein at least some of thelight guides are substantially co-planar.
 5. The luminaire of claim 4,wherein all of the light guides are substantially co-planar.
 6. Aluminaire, comprising: a framework comprising a plurality ofinterconnected support members; a plurality of light guides attached tothe framework, each of the light guides having opposed major surfaces,at least one of the major surfaces of each light guide havingdiffractive surface features therein adapted to couple guided-mode lightout of the light guide; and a plurality of light sources disposed onand/or in the support members, the light sources being distributed toinject light into all of the light guides; wherein at least some of thelight guides are arranged in a helix.
 7. A luminaire, comprising: aframework comprising a plurality of interconnected support members; aplurality of light guides attached to the framework, each of the lightguides having opposed major surfaces, at least one of the major orsurfaces of each light guide having diffractive surface features thereinadapted to couple guided-mode light out of the light guide; and aplurality of light sources disposed on and/or in the support members,the light sources being distributed to inject light into all of thelight guides; wherein at least some of the light guides collectivelyform a concave shape.
 8. A luminaire, comprising: a framework comprisinga plurality of interconnected support members; a plurality of lightguides attached to the framework, each of the light guides havingopposed major or surfaces, at least one of the major surfaces of eachlight guide having diffractive surface features therein adapted tocouple guided-mode light out of the light guide; and a plurality oflight sources disposed on and/or in the support members, the lightsources being distributed to inject light into all of the light guides;wherein the light guides collectively form a 3-dimensional structurethat is closed and hollow.
 9. A lunnuaire, comprising: a frameworkcomprising a plurality of interconnected support members; a plurality oflight guides attached to the framework, each of the light guides havingopposed major surfaces, at least one of the major surfaces of each lightguide having diffractive surface features therein adapted to coupleguided-mode light out of the light guide; and a plurality of lightsources disposed on and/or in the support members, the light sourcesbeing distributed to inject light into all of the light guides; whereinthe plurality of light sources include light sources of substantiallydifferent first, second, and third output colors, and wherein the lightsources are distributed such that at least a first one of the lightguides is illuminated predominantly with light source(s) of the firstoutput color, at least a second one of the light guides is illuminatedpredominantly with light source(s) of the second output color, and atleast a third one of the light guides is illuminated predominantly withlight source(s) of the third output color.
 10. A luminaire, comprising:a plurality of light guides, each of the light guides having opposedmajor surfaces, at least one of the major surfaces of each light guidehaving diffractive surface features therein adapted to coupleguided-mode light out of the light guide; and a plurality of lightsources configured to inject light into the plurality of light guides;wherein at least sonic of the light guides are arranged in a helix. 11.A luminaire, comprising: a plurality of light guides, each of the lightguides having opposed major surfaces, at least one of the major surfacesof each light guide having diffractive surface features therein adaptedto couple guided-mode light out of the light guide; and a plurality oflight sources configured to inject light into the plurality of lightguides; wherein the light guides collectively form a concave shape. 12.The luminaire of claim 11 wherein the concave shape is an open concaveshape.
 13. A luminaire of claim 11, wherein the concave shape is atubular shape with open ends.
 14. A luminaire, comprising: a pluralityof light guides, each of the light guides having opposed major surfaces,at least one of the major surfaces of each light guide havingdiffractive surface features therein adapted to couple guided-mode lightout of the light guide; and a plurality of light sources configured toinject light into the plurality of light guides; wherein the lightguides collectively form a 3-dimensional structure that is closed andhollow.
 15. A luminaire, comprising: a tube-shaped light guide, thelight guide having a first major surface on which diffractive surfacefeatures are formed, the diffractive surface features adapted to coupleguided-mode light out of the light guide; and a first light sourceconfigured to inject light into the light guide.
 16. The luminaire ofclaim 15, wherein the tube-shaped light guide is hollow and has two openends and an annular-shaped side surface proximate one of the open ends.17. The luminaire of claim 16, wherein the first light source isdisposed to inject light into the annular-shaped side surface.
 18. Theluminaire of claim 15, wherein the tube-shaped light guide issubstantially cylindrical in shape.
 19. The luminaire of claim 15,wherein the tube-shaped light guide is substantially conical in shape.20. An optical device, comprising: a light guide having opposed majorsurfaces, at least one of the major surfaces having diffractive surfacefeatures therein adapted to couple guided-mode light out of the lightguide; and a patterned low index subsurface layer configured toselectively block some guided mode light from reaching at least some ofthe diffractive surface features.
 21. The device of claim 20, whereinthe patterned low index subsurface layer comprises first and secondlayer portions, the first layer portions comprising nanovoided polymericmaterial.
 22. The device of claim 21, wherein the second layer portionscomprise the nanovoided polymeric material and an additional material.23. The device of claim 21, wherein the second layer portions comprise apolymer material that is not nanovoided.
 24. The device of claim 20 thepatterned low index subsurface layer is composed of one or more polymermaterials none of which are nanovoided.
 25. The device of claim 20,further comprising a light source disposed to inject light into thelight guide.